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

int main(void)
{
int num = 100000;
int index = 0;
double pi = 0.0;

while (index < num) {
pi += 4.0 * pow(-1.0, (double)index) / (double)(index * 2 + 1);
index++;
}
printf("pi = %f\n", pi);

return 0;
}