C

import math


def main():
    n, a1, b, mx = map(int, input().split())
    x = None
    if b > 1:
        exp = (mx * (b - 1)) / a1 + 1
        x = math.ceil(math.log(exp, b))
    if b == 1:
        x = round(mx/a1)+1
    if x > n:
        print(n)
    else:
        print(x-1)


if __name__ == "__main__":
    main()