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",&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\n",pi);
}
return 0;
}