include<stdio.h>

main()
{int n,i,k=1,sum=0,sign=1;
double m=0.0;
scanf("%d",&n);
for(i=1;i<=n;i++)
{sum=sum+sign*(2*k-1);
 m+=1.0/sum;
 sign*=-1;
 k++;}
 printf("%.3lf",m);}