#include<iostream> using namespace std; int main(){ int n; cin >> n; long long a[50] = {0}; a[0] = 1; a[1] = 2; a[2] = 4; for(int i = 4 ; i <= n ; i++){ a[i] = a[i-3]+a[i-2]+a[i-1]; } cout << a[n]; return 0; }