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

double f(double x, double y) { return sqrt(x * x + y * y); }

int g(int s, int n) {
  return (n == 0) ? s
                  : (f((double)rand() / RAND_MAX, (double)rand() / RAND_MAX)) < 1.0
                    ? g(s + 1, n - 1)
                    : g(s, n - 1);
}

#define SEED 31415926
#define N 100000
int main() {
  srand(SEED);
  printf("%f\n", 4.0 * g(0, N) / N);
  return 0;
}
/* end */