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

int main()
{
    float pi = (4.0/1.0) - (4.0/3.0) + (4.0/5.0) - (4.0/7.0) + (4.0/9.0) - (4.0/11.0) + (4.0/13.0) - (4.0/15.0);
    printf("%f", pi);
}