杭电ACM----2018母牛的故事

#include <iostream>

using namespace std;

int main()

{

    int n;

    int a[56]={0,1,2,3};

    while(cin>>n&&n)

    {

        switch(n)

        {

            case 1:

                cout<<a[n]<<endl;

                break;

            case 2:

                cout<<a[n]<<endl;

                break;

            case 3:

                cout<<a[n]<<endl;

                break;

            default:



                    for(int i=4;i<56;i++)

                    a[i]=a[i-1]+a[i-3];

                    cout<<a[n]<<endl;



                    break;



        }

    }



}