poj2521

简单题

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
using namespace std;

int main()
{
    //freopen("D:\\t.txt", "r", stdin);
    int m, p, n, c;
    while (scanf("%d%d%d%d", &n, &m, &p, &c) != EOF && !(n == 0 && m == 0 && p == 0 && c == 0))
        printf("%d\n", -(m - n - p));
    return 0;
}