POJ 2521

 1 #include <iostream>
 2 #include <stdio.h>
 3 using namespace std;
 4 
 5 int main()
 6 {
 7     //freopen("acm.acm","r",stdin);
 8     int a;
 9     int b;
10     int c;
11     int d;
12     int ans;
13     do
14     {
15         cin>>a>>b>>c>>d;
16         if(!a&&!b&&!c&&!d)
17         {
18             break;
19         }
20         ans = (b - c - a)*(-1);
21         cout<<ans<<endl;
22     }
23     while(1);
24 }