#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define N 1000000000

int main (int argc, char** argv)
{
    long long int n;
    long long int i;
    double l_sum, x, h;

    n=N;

    if(argc==2)
    {
        n=atoll(argv[1]);
    }



    h = 1.0/n;

    l_sum = 0.0;
    
    for (i = 0; i < n; i ++)
    {
        x = (i+0.5)*h;
        l_sum += 4.0/(1.0 + x*x);
    }

    l_sum *= h;

    printf("N=%lld, PI = %0.20g\n",n ,l_sum);

    return 0;
}