1041

#include<stdio.h>
#include<math.h>
int main()
{
    int n,i;
    double sum,a;
    scanf("%d",&n);
    sum=0.0;
    a=1.0; 
    for(i=1;i<=(2*n-1);i+=2)
       {
        sum+=a/i;
        a=-a;
        
       }
 
    printf("%.2f",sum);
     
     
    return 0;
     
     
}