#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main(void)
{ int n=1;
double eps=1e-5,x,c=1,z,a,q,sum=0;
 
 scanf("%lf", &x);
 q=x;
 
 
 while(fabs(a) > eps)
 { c*=x-1;
z=n*q;
a=c/z;
sum+=a;
n++;
q*=q;
}

    
         printf("\n\n\n %lf\n", sum);


  
  system("PAUSE");	
  return 0;
}