#include <iostream>
using namespace std;
int main() {
int n, m, x, y;
cin >> n >> m >> x >> y;
if (n > m){
if ((m - x) < x){
x = m - x;
}
if ((n - y) < y){
y = n - y;
}
} else {
if ((n - x) < x){
x = n - x;
}
if ((m - y) < y){
y = m - y;
}
}
if (x > y){
cout << y << endl;
} else{
cout << x << endl;
}
return 0;
}
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