#include <bits/stdc++.h>
using namespace std;
INT main()
{
    LONG LONG m,n,x,y;
    cin >> n >> m >> x >> y;
    LONG LONG a = (x - 1) * m;
    IF(x % 2 != 0){
        a = a + y - 1;
    }
    ELSE{
        a = a + m - y;
    }
    cout << a;
}