# include <stdio.h>
# include <string.h>
# include <iostream>
# include <algorithm>
// # include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
const int M = 5e5 + 10;
const int mod = 1e9+7;

# define RG register
# define ST static

int n, m, x, y, ans;

int main() {
    while(~scanf("%d%d%d%d", &n, &m, &x, &y)) {
        if(n > m) swap(n, m), swap(x, y);
        x = min(x, n-x+1), y = min(y, m-y+1);
        if(n == m && (n&1) && x == (n+1)/2 && x == y) ans = x-1;
        else ans = max((n+1)/2, min(n-x, y));
        printf("%d\n", ans);
    }
    return 0;
}