MOD = 998244353
a,b,p,q = map(int,input().split())

T = 2*10**5
memo = {}
f = lambda x,y: (y,(a*y-b*x)%MOD)
B = (q,p)
for i in range(T):
    memo[B] = i
    B = f(*B)

v,w = (1,0),(0,1)
for _ in range(T):
    v,w = f(*v),f(*w)
c1,c2 = v
c3,c4 = w
g = lambda x,y: ((c1*x+c3*y)%MOD,(c2*x+c4*y)%MOD)

s = f(2,a)
for j in range(1,T+1):
    s = g(*s)
    if s in memo:
        i = memo[s]
        print(j*T-i+2)
        exit()