#include<bits/stdc++.h> using namespace std; int main() { unsigned long long a[114514]; int n; a[1]=1; a[2]=2; a[3]=4; for(int i=4;i<=73;i++) a[i]=a[i-1]+a[i-2]+a[i-3]; while(cin>>n) cout<<a[n]<<endl; }