#include<iostream>
#include<iomanip>
#include<cmath>
#include<cstring>
#include<algorithm>
using namespace std;
int main(){
    int n,i;
    float fn,a1=1.0,a2=1.0;
    cin>>n;
    for(i=1;i<=n;i++){
        a1*=1+sqrt(5)/2;
        a2*=1+sqrt(5)/2;
    }
    fn=(a1-a2)/sqrt(5);
    cout<<setprecision(2)<<fixed<<fn<<endl;
    return 0;
}

再继续问就真的精通MD了