include <bits/stdc++.h>

using namespace std; int main() { unsigned long long F[75]; F[0]=0; F[1]=1; F[2]=2; F[3]=4; for(int i=4; i<=73; i+=1) F[i]=F[i-3]+F[i-2]+F[i-1]; for(int n; scanf("%d",&n)!=EOF;) printf("%llu\n",F[n]); return 0; }