#include <bits/stdc++.h> using namespace std; long long a[50] = {0,1,2,4} int main() { int n,a=1,b=2,c=4,d; cin>>n; for(int i=4;i<=n;i++){ a[i] = a[i-1]+a[i-2]+a[i-3]; } cout<<a[n]<<endl; return 0; }