#include<stdio.h>

#include<math.h>

main()

{float pi=0,n=1,t=1;

int s=1;

while(fabs(t)>=1e-4)

{pi=pi+t;

n=n+2;

s=-s;

t=s/n;

}

pi=pi*4;

printf("pi=%f",pi);

}