a = int(input())
b = int(input())
c = int(input())
d = int(input())
i = 0

def nod(n,m):
    while (n != 0) and (m != 0):
        if n > m:
            n = n % m
        else:
            m = m % n
    return(n + m)

while a < c and b < d:
    a += 1
    b += 1
    i += 1
    if a == c and b == d:
        break
    a = a / nod(a,b)
    b = b / nod(a,b)