#include <bits/stdc++.h>

int ri() {
	int n;
	scanf("%d", &n);
	return n;
}

int main() {
	int64_t a, b, c, d;
	std::cin >> a >> b >> c >> d;
	if (a > b) {
		int64_t cnt = (a - b) / (c + 1);
		a -= c * cnt;
		b += cnt;
		while (std::min(a, b) < std::min(a - c, b + 1)) a -= c, b++;
	} else {
		int64_t cnt = (b - a) / (d + 1);
		a += cnt;
		b -= d * cnt;
		while (std::min(a, b) < std::min(a + 1, b - d)) b -= d, a++;
	}
	printf("%" PRId64 "\n", std::min(a, b));
	return 0;
}