import sys
import math

data = sys.stdin.read().split()
x1 = int(data[0])
y1 = int(data[1])
x2 = int(data[2])
y2 = int(data[3])
dx = abs(x2 - x1)
dy = abs(y2 - y1)
ans = math.gcd(dx, dy) + 1
print(ans)