otrezok

x1, y1, x2, y2 = map(int, input().split())


x = abs(x2 - x1)
y = abs(y2 - y1)

if x == 0 or y == 0:
    print(max(x, y) + 1)
else:
    a, b = x, y
    while a % b > 0:
        a, b = b, a % b
    print(b + 1)