#include<iostream>
#include<iomanip>
using namespace std;
double fibb(long n){
if(n<1){
return -1;
}
long F[n+1];
F[1]=1;
F[2]=1;
for(int i=3;i<=n;i++){
F[i]=F[i-1]+F[i-2];
}
return F[n];
}
int main(){
long num;
cin>>num;
if(num<20){
cout<<setprecision(8)<<fixed<<fibb(num)/fibb(num+1)<<endl;
}else{
cout<<"0.61803399"<<endl;
}
return 0;
}