include <stdio.h>

 int main(){

     double eps, sum=, i, temp=;

     scanf("%le", &eps);

     for(i=; temp>eps; i++){

         temp = temp*i/(*i+);

         sum += temp;

     }

     printf("PI = %.5f\n", *sum);

     return ;

 }

 include<stdio.h>

 int main() {

     int fz=,fm=,k=;

     double t=1.0,pi=1.0,eps;

     scanf("%le",&eps);

     while(t>=eps) {

         fz*=k;

         fm*=(*k+);

         t = (double)fz/fm;

         pi += t;

         k++;

     }

     printf("%lf",*pi);

 }