#include <bits/stdc++.h> using namespace std; int n; unsigned long long visited[80] = {0, 1, 2, 4}; unsigned long long dfs(int x) { if(!visited[x]) visited[x] = dfs(x-1)+dfs(x-2)+dfs(x-3); return visited[x]; } int main() { while(cin>>n) cout << dfs(n) << '\n'; return 0; }