#include<iostream> #include<cmath> #include<cstdio> #include<cstring> using namespace std; int main() { long long n; long long a[21] = {0,3,7,17}; cin >> n; for(int i = 3;i <= n;i++) a[i] = a[i - 1] * 2 + a[i-2]; cout << a[n] << endl; return 0; }