C

import math
n,a,b,m = [int(i) for i in input().split()]
c = 0
if b != 1:
    try:
        c = math.floor(math.log((m*(b-1)+a)/a, b))
        #print('a')
    except OverflowError:
        #print('b')
        c = math.floor(math.log((m*(b-1)+a)//a, b))
else:
    c = m//a
if c > n:
    c = n
print(c)