require 'prime'

N, K, M = gets.split.map(&:to_i)
ans = Float::INFINITY

def f(n, k, r, e, c)
  cnt = 0

  while n > 0
    n /= e
    cnt += n
  end

  while k > 0
    k /= e
    cnt -= k
  end

  while r > 0
    r /= e
    cnt -= r
  end

  cnt / c
end

M.prime_division.each do |e, c|
  v = f(N, K, N - K, e, c)

  ans = v if ans > v
end

puts ans