#include <iostream>
using namespace std;
int main() {
  // put your code here
    int N, M, X, Y, a, b;
    cin >> N >> M >> X >> Y;
    if (M > N) {
        N = M + N;
        M = N - M;
        N = N - M;

    }
    if (X < Y) {
        a = X;
    }
    else {
        a = Y;
    }
    if (M - X < N - Y) {
        b = M - X;
    }
    else {
        b = N - Y;
    }
    if (a < b) {
        cout << a;
    }
    else {
        cout << b;
    }

}