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

int main() {

  int N=1000;
  int i;
  double sum=0.0;
  for(i=0; i<N; i++) {
    double x = 1.0/N*i;
    sum = sum+sqrt(1-x*x)/N;
  }
  printf ("result is %g\n", sum*4);
  return 0;
}