#include<bits/stdc++.h> using namespace std; long long a[51]; int main(){ int n; cin >> n; if(n<4) { a[1] = 1; a[2] = 2; for(int i = 3;i <= n;i++){ a[i] = a[i-1]+a[i-2]; } cout << a[n]+1; }else{ cout<<(n-2)*4; } return 0; }