#include<iostream> #include<cstdio> #include<cstring> #include<cmath> using namespace std; int main(){ long long a[41] = {0, 1, 2, 4}; int n; long long q = 0; cin >> n; if (n==0) { cout<<0; return 0; } else{ for (int i = 4; i <=n; i++) { a[i] = a[i-3] + a[i-1] + a[i-2]; } cout << a[n]; } return 0; }