import math
n, a, b, maxxm = map(int, input().split())
l=0
r=min(n, int(math.ceil(math.log(maxxm, b))) if b!=1 else (maxm+a-1)//a)+1
while (r>1+l):
    m=(l+r)//2
    flag=0
    if (b!=1):
        flag=a*(b**m-1)//(b-1)
    else:
        flag=a*m
    if (flag<=maxxm):
        l = m
    else:
        r = m
print(l)