#include <stdio.h>

int main(void) {
	// your code goes here
    int n=1,sign=1;
    double pi=0,term=1;
    do 
    {  pi=pi+term;
       sign=-sign;
       n=n+2;
       term=sign*1/n;
    } while(fabs(term)>=1e-6);
    pi=pi*4;
    printf("pi=%10.8f\n",pi);
	return 0;
}