diff --git a/2025.05.09/12Ex/solve.c b/2025.05.09/12Ex/solve.c
index d75d2e3..93ff32e 100644
--- a/2025.05.09/12Ex/solve.c
+++ b/2025.05.09/12Ex/solve.c
@@ -10,36 +10,50 @@ int t12_solve (
 		double (*yt) (double),
 		double a, double b,
 		double eps, double *res
-) {
+) {	
 	int it;
+	
+	double xa = xt(a), ya = yt(a);
+	double xb = xt(b), yb = yt(b);
+	double xl = xa, yl = yb;
 
-	int n = 1;
+	int n = 2;
 	double h = (b - a) * 0.5;
-	double x = xt(b) - xt(a);
-	double y = yt(b) - yt(a);
+	double x = xb - xl;
+	double y = yb - yl;
 	double len_n = sqrt(x * x + y * y);
 
 	for (it = 1; it <= MAX_ITER; ++it)
 	{
-		double t = a;
 		double tn = a + h;
 		double len_2n = 0;
-	
-		for (int i = 0; i < n; i++)
-		{
-			x = xt(tn) - xt(t);
-			y = yt(tn) - yt(t);
-			len_2n += sqrt(x * x + y * y);
 
-			t = tn;
+		for (int i = 1; i < n; i++)
+		{
+			double xc = xt(tn);
+			double yc = yt(tn);
+
+			x = xc - xl;
+			y = yc - yl;
+			len_2n += sqrt(x * x + y * y);
+			
+			xl = xc;
+			yl = yc;
 			tn += h;
 		}
 
+		x = xb - xl;
+		y = yb - yl;
+		len_2n += sqrt(x * x + y * y);
+
 		h *= 0.5;
 
 		if (fabs(len_2n - len_n) < eps)
 			break;
 		
+		xl = xa;
+		yl = ya;
+
 		len_n = len_2n;
 		n <<= 1;
 	}
diff --git a/2025.05.09/dist/Krivoruchenko_SK/.nfs000000000e4a0ec40000000a b/2025.05.09/dist/Krivoruchenko_SK/.nfs000000000e4a0ec40000000a
new file mode 100644
index 0000000..cdc8913
Binary files /dev/null and b/2025.05.09/dist/Krivoruchenko_SK/.nfs000000000e4a0ec40000000a differ
diff --git a/2025.05.09/dist/Krivoruchenko_SK/Makefile b/2025.05.09/dist/Krivoruchenko_SK/Makefile
index 40f7fca..11c07fb 100644
--- a/2025.05.09/dist/Krivoruchenko_SK/Makefile
+++ b/2025.05.09/dist/Krivoruchenko_SK/Makefile
@@ -2,7 +2,7 @@ FLAGS = -fstack-protector-all -W -Wall -Wextra -Wunused -Wcast-align -Werror -pe
 
 OBJ_COMMON = solve.o
 
-NUMS = 1 2 3 4 5 6 7 8 9 10 11
+NUMS = 1 2 3 4 5 6 7 8 9 10 11 12
 
 OUTS = $(foreach n,$(NUMS),$(shell printf "a%02d.out\n" "$(n)"))
 
diff --git a/2025.05.09/dist/Krivoruchenko_SK/a12.c b/2025.05.09/dist/Krivoruchenko_SK/a12.c
new file mode 100644
index 0000000..58012bf
--- /dev/null
+++ b/2025.05.09/dist/Krivoruchenko_SK/a12.c
@@ -0,0 +1,45 @@
+#include <stdio.h>
+#include <time.h>
+#include <math.h>
+#include <float.h>
+
+#include "init_f.h"
+#include "solve.h"
+
+/* ./a12.out a b eps k_x k_y */
+int main (int argc, char *argv[])
+{
+	double t, integral, a, b, eps;
+	int x, y, n, calls, task = 12;
+	
+	double (*f_lst[]) (double) = {f0, f1, f2, f3, f4, f5, f6};
+	int len_f = sizeof(f_lst) / sizeof(f_lst[0]);
+
+	if (
+			!((argc == 6) && 
+			sscanf(argv[1], "%lf", &a) == 1 &&
+			sscanf(argv[2], "%lf", &b) == 1 &&
+			((sscanf(argv[3], "%lf", &eps) == 1) && (eps > 0)) &&
+			((sscanf(argv[4], "%d", &x) == 1) && ((0 <= x) && (x < len_f))) &&
+			((sscanf(argv[5], "%d", &y) == 1) && ((0 <= y) && (y < len_f))))
+	) {
+		fprintf(stderr, "Usage: %s a b eps k_x k_y\n", argv[0]);
+		return -1;
+	}
+
+
+	t = clock();
+	n = t12_solve(f_lst[x], f_lst[y], a, b, eps, &integral);
+	t = (clock() - t) / CLOCKS_PER_SEC;
+	
+	calls = get_call_count();
+
+	if (n < 0) {
+		fprintf (stdout, "%s : Task = %d Method is not applicable Count = %d T = %.2f\n", argv[0], task, calls, t);
+		return -2;
+	} else {
+		fprintf (stdout, "%s : Task = %d Res = %e N = %d Count = %d T = %.2f\n", argv[0], task, integral, n, calls, t);
+		return 0;
+	}
+}
+
diff --git a/2025.05.09/dist/Krivoruchenko_SK/solve.c b/2025.05.09/dist/Krivoruchenko_SK/solve.c
index 4904d8f..94d0ca9 100644
--- a/2025.05.09/dist/Krivoruchenko_SK/solve.c
+++ b/2025.05.09/dist/Krivoruchenko_SK/solve.c
@@ -315,3 +315,64 @@ double t11_solve (
 }
 
 // -------
+
+int t12_solve (
+		double (*xt) (double), 
+		double (*yt) (double),
+		double a, double b,
+		double eps, double *res
+) {	
+	int it;
+	
+	double xa = xt(a), ya = yt(a);
+	double xb = xt(b), yb = yt(b);
+	double xl = xa, yl = yb;
+
+	int n = 2;
+	double h = (b - a) * 0.5;
+	double x = xb - xl;
+	double y = yb - yl;
+	double len_n = sqrt(x * x + y * y);
+
+	for (it = 1; it <= MAX_ITER; ++it)
+	{
+		double tn = a + h;
+		double len_2n = 0;
+
+		for (int i = 1; i < n; i++)
+		{
+			double xc = xt(tn);
+			double yc = yt(tn);
+
+			x = xc - xl;
+			y = yc - yl;
+			len_2n += sqrt(x * x + y * y);
+			
+			xl = xc;
+			yl = yc;
+			tn += h;
+		}
+
+		x = xb - xl;
+		y = yb - yl;
+		len_2n += sqrt(x * x + y * y);
+
+		h *= 0.5;
+
+		if (fabs(len_2n - len_n) < eps)
+			break;
+		
+		xl = xa;
+		yl = ya;
+
+		len_n = len_2n;
+		n <<= 1;
+	}
+
+	if (it > MAX_ITER) 
+		return -1;
+	
+	*res = len_n;
+
+	return n;
+}
diff --git a/2025.05.09/dist/Krivoruchenko_SK/solve.h b/2025.05.09/dist/Krivoruchenko_SK/solve.h
index d51d8bb..d92d8fd 100644
--- a/2025.05.09/dist/Krivoruchenko_SK/solve.h
+++ b/2025.05.09/dist/Krivoruchenko_SK/solve.h
@@ -100,4 +100,11 @@ double t11_solve (
 
 // -------
 
+int t12_solve (
+		double (*x) (double), 
+		double (*y) (double),
+		double a, double b,
+		double eps, double *res
+);
+
 #endif