public class Main {
    public static void main(String[] args) {
        double pi = 0.0;
        int z = 1;

        for (int i = 1; i <= 2000000000; i++)
        {
            pi += (1.0 / ((i*2)-1)) * z;
            z *= -1;
        }

        System.out.println(pi*4);
    }
}

#include <stdio.h>

int main(void)
{
    double pi = 0.0;
    int z = 1, i;

    for (i = 1; i <= 2000000000; i++)
    {
        pi += (1.0 / ((i*2)-1)) * z;
        z *= -1;
    }

    printf("%.15f\n", pi*4);
}