C1,C2,C3

import math
n,a1,b,mx=map(int,input().split())



if a1<=mx and a1!=0:
    if b!=1:
        osn = (mx * (b - 1)) // a1 + 1
        pp=int(math.log(osn,b))
    else:
        pp=int(mx//a1)
    if pp >= n:
        print(n)
    else:
        print(pp)
else:print(0)