终于AC了.步长应该用最小的.
#include<iostream>
using namespace std;
int main()
 {
    int p,e,i,d,x,n,s;
    cin>>p>>e>>i>>d;
    n=1;
    while(!(p==-1&&e==-1&&i==-1&&d==-1))
    {
       s=p; if(s>e) s=e; if(s>i) s=i; if(s>d) s=d;
       p=p-s; e=e-s; i=i-s; d=d-s;
       if(p==0&&e==0&&i==0)
        x=21252-d;
       else
        {
           x=p;
         if (p==0)
          x=+23;
          while(!((x-e)%28==0&&(x-i)%33==0))
           x+=23;
           x=x-d;
           }    
         if(x>21252) x=x-21252;
         if(x<0) x=x+21252 ;
          cout<<"Case "<<n<<": the next triple peak occurs in "<<x<<" days."<<endl;
          n++;
         cin>>p>>e>>i>>d; 
         }
       return 0;
}