#include<stdio.h>
int main(){
int N ;
scanf("%d",&N);
double a =2;
double b = 1;
int i = 0;
double sum = 0;
for(i=0;i<N;i++){
sum+=1.0*a/b;
double t = a;
a = a + b;
b = t;
}
printf("%.2lf",sum);
}
#include<stdio.h>
int main(){
int N ;
scanf("%d",&N);
int a =2;
int b = 1;
int i = 0;
double sum = 0;
for(i=0;i<N;i++){
sum+=1.0*a/b;
int t= a;
a = a + b;
b = t;
}
printf("%.2lf\n",sum);
}