#include "bits/stdc++.h"
#define int long long
using namespace std;
using ll = long long;
using P = pair<ll, ll>;
const ll INF = (1LL << 61);
ll mod = 998244353;

signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	int A, B, N, M; cin >> A >> B >> N >> M;
	if (A > B) {
		int cnt = (A - B) / N;
		A -= cnt * N;
		B += cnt;
		int ans = max(min(A, B), max(min(A - N, B + 1), min(A + N, B - 1)));
		cout << ans << endl;
	}
	else {
		int cnt = (B - A) / M;
		B -= cnt * M;
		A += cnt;
		int ans = max(min(A, B), max(min(A + 1, B - M), min(A - 1, B + M)));
		cout << ans << endl;
	}
	return 0;
}