#include<iostream>
#include<algorithm>

int main() {
	int gx, gy, ex, ey;

	std::cin >> gx >> gy >> ex >> ey;

	int ans = 0;
	if (ex == ey){
		if (gx > gy) {
			gx -= 1;
		} else {
			gy -= 1;
		}
		ans++;
	}
	if (gx > gy) {
		gx -= gy;
		ex -= gy;
		ey -= gy;
		ans += gy;
		gy = 0;
	} else {
		gy -= gx;
		ey -= gx;
		ex -= gx;
		ans += gx;
		gx = 0;
	}

	ans += std::max(gx, gy);
	if (ey < 0 || ex < 0) {
		std::cout << ans << std::endl;
		return 0;
	}
	std::cout << ans  << std::endl;
	return 0;

}