strr = input()
strr = strr.split(' ')
n = int(strr[0])
a1 = int(strr[1])
b = int(strr[2])
MAX = int(strr[3])
if b == 1:
    print(min((MAX // a1), n))
else:
    k = MAX*(b-1)//a1
    k += 1
    ans = 0
    while k//b > 0:
        k //= b
        ans += 1
    print(min(ans, n))