你这样有可能得到负的，而且速度也慢吧
> #include <iostream>
> using namespace std;
> int main()
> { long p,e,i,d;
>   long a;
>   long number=1;
>   while(cin>>p>>e>>i>>d){
> 	  if(p==-1 && e==-1 && i==-1 && d==-1) break;
> 	  for(a=1;;a++){
> 		  if((a-p)%23==0 && (a-e)%28==0 && (a-i)%33==0){
> 			  cout<<"Case "<<number<<": the next triple peak occurs in "<<a-d+1<<" days."<<endl;
> 			  number++;
> 		      break;
> 		  }
> 	  }
>   }
>   return 0;
> }