ABC121A - White Cells

問題：A - White Cells

#include <algorithm>
#include <iostream>
using namespace std;

int main(void) {
    int h, w, selh, selw;

    cin.tie(0);
    ios::sync_with_stdio(false);
    cin >> h >> w;
    cin >> selh >> selw;
    cout << (h - selh) * (w - selw) << "\n";
    return 0;
}