mnogougolnik

n = int(input())
dots = []
while n:
    dots.append(tuple(map(int, input().split())))
    n -= 1

res = 0

for i in range(len(dots)):
    x = abs(dots[i][0] - dots[i-1][0])
    y = abs(dots[i][1] - dots[i-1][1])
    if min(x, y) == 0:
        res += max(x, y)
    else:
        while x % y > 0:
            x, y = y, x % y
        res += y

print(res)