题解

#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,f[1111111];
    f[0]=1,f[1]=1,f[2]=2;
    while(1){
        cin>>n;
        if(n==0) break;
        for(int i=3;i<=n;i++)f[i]=f[i-1]+f[i-2]+f[i-3];
        cout<<f[n]<<endl;
    }
    return 0;
}