import sys


def input(): return sys.stdin.readline().rstrip('\n')


def sgn(x):
    if x < 0:
        return -1
    if x == 0:
        return 0
    return 1


def main():
    x, y = map(int, input().split())
    x2, y2 = map(int, input().split())

    if abs(x) == abs(y) and abs(x2) == abs(y2) and sgn(x) == sgn(x2) and sgn(y) == sgn(y2):
        print(abs(x)+1)
    else:
        print(max(abs(x), abs(y)))


if __name__ == '__main__':
    main()