## https://yukicoder.me/problems/no/1443

import heapq


def main():
    N, M, P = map(int, input().split())
    A = list(map(int, input().split()))

    max_a = max(A)

    answer = float("inf")
    for a in A:
        a1 = a
        x = 0
        while a1 % P == 0:
            x += 1
            a1 //= P

        if a <= M and a1 == 1:
            continue

        y = 1
        cost = 0
        while y * max_a <= M and y * a <= M:
            y *= a1
            cost += 1 + x
        
        answer = min(answer, cost + 1)
    if answer == float("inf"):
        print(-1)
    else:
        print(answer)
            





if __name__ == "__main__":
    main()