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;

         }
     }

 }