import math

def calc(a, b, n):
    if a == 1 and b == 1:
        return n
    elif b != 1:
        return a * ((b**n) - 1) // (b-1)
    else:
        an = a + (n-1) * (a*b - a)
        sn = ((a + an)//2)*n
        return sn

n, a, b, m = map(int, input().split())

if b != 1:
    d = int(math.log((m // a), b)) + 1
else:
    d = m // a

if calc(a, b, d + 1) <= m:
    if d + 1 >= n:
        print(n)
    else:
        print(d + 1)
elif calc(a, b, d) <= m:
    if d >= n:
        print(n)
    else:
        print(d)
elif calc(a, b, d - 1) <= m:
    if d - 1 >= n:
        print(n)
    else:
        print(d - 1)