import math
def des():
    n,b1,q,m = map(int,input().split())
    if q==1:
            return min(n,m//b1)
    m*= (1-q)
    m//=b1
    m = 1 - m
    s = math.floor(math.log(m,q))
    return min(s,n)
print(des())