π

#include<stdio.h>
#include<math.h>
int main(void)
{
    int denominator,flag,n;
    double item,pi;
    flag=1;
    denominator=1;
    item=1.0;
    pi=0;

    scanf("%d
",&n);
    if(n<3||n>8)
        printf("error");
    while(n!=0){
        while(fabs(item)>=pow(10,-n)){
          item=flag*1.0/denominator;
          pi=pi+item;
          flag=-flag;
          denominator=denominator+2;
        }
        pi=pi*4;
        scanf("%d",&n);
        printf("%.6f
",pi);
    }
    return 0;
}