geom3

#define fixlen 10000

#include <stdio.h>
#include <math.h>

double getCos(double x, double y, double x1, double y1, double x2, double y2);
double getVisionAngle(double* px, double* py, int len);

int main(void)
{
	double pointsX[fixlen], pointsY[fixlen], a;

	FILE *fin;
	int len = 0;
	fin = fopen("input.txt", "r");

	if (!fin)
    {
		printf("File opening error\n");
		return -1;
	}

	for (int i = 0; i < fixlen; i++)
	{
		if (fscanf(fin, "%lf", &a) != 1) break;
		pointsX[i] = i;
		if (fscanf(fin, "%lf", &a) != 1) break;
		pointsY[i] = i;
		len++;

	}
	printf("%lf" , getVisionAngle(pointsX, pointsY, len));
	fclose(fin);

	return 0;
}

double getCos(double x, double y, double x1, double y1, double x2, double y2)
{
	double a, b, c, cos;
	a = pow((x1-x2), 2) + pow((y1-y2), 2);
	b = pow((x-x2), 2) + pow((y-y2), 2);
	c = pow((x1-x), 2) + pow((y1-y), 2);
	cos = (b + c - a) / (2 * sqrt(b*c));
	return cos;
}

double getVisionAngle(double* px, double* py, int len)
{
	double x, y, mincos, curcos, x1, x2, y1, y2;

	scanf("%lf %lf", &x, &y);
	mincos = 2;
	for (int i = 0; i < len - 1; i++)
    {
		for (int j = i + 1; j < len; j++)
		{
            x1 = px[i];
            y1 = py[i];
            x2 = px[j];
            y2 = py[j];
			curcos = getCos(x, y, x1, y1, x2, y2);
			if (curcos < mincos) mincos = curcos;
		}
	}
	mincos = acos(mincos);
	return mincos;
}