(｡･∀･)ﾉﾞ嗨AT上楼梯

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; }