#include <bits/stdc++.h>
using namespace std;
long long louties[4]={0,1,2,3};
int louti , v = 0 , v1 ,v2;
void dfs(int d){
    if(d == louti){
        cout << v << endl;
        return ;
    }
    else{
        if(d == 3){
            v1 = louties[d];
            v2 = louties[d - 1];
        }else{
            int v3 = v1;
            v1 = v;
            v2 = v3;
        }
        v += (v1 + v2);
        dfs(d + 1);
    }
}
int main(){
    cin >> louti;
    if(louti <4){cout << louties[louti - 1];return 0;}
    dfs(3);
}