#include <stdio.h>
#include <stdlib.h>
#define rep(i, n) for (i = 0; i < n; i++)
#define max(a, b) (a > b ? a : b)
#define sign(a) (a == 0 ? 0 : (a > 0 ? 1 : -1))

int main() {
	int x, y, x2, y2;
	scanf("%d %d %d %d", &x, &y, &x2, &y2);

	int ans = max(x, y);
	if (x == y && x2 == y2 &&
		abs(x2) < abs(x) && abs(y2) < abs(y) &&
		sign(x) == sign(x2) && sign(y) == sign(y2)) ans++;

	printf("%d\n", ans);
	return 0;
}