#line 1 "main.cpp"

/**
 * @title Template
 */

#include <iostream>
#include <algorithm>
#include <utility>
#include <numeric>
#include <vector>
#include <array>
#include <cassert>

#line 2 "/Users/kodamankod/Desktop/cpp_programming/Library/other/range.cpp"

#line 4 "/Users/kodamankod/Desktop/cpp_programming/Library/other/range.cpp"

class range {
  struct iter {
    std::size_t itr;
    constexpr iter(std::size_t pos) noexcept: itr(pos) { }
    constexpr void operator ++ () noexcept { ++itr; }
    constexpr bool operator != (iter other) const noexcept { return itr != other.itr; }
    constexpr std::size_t operator * () const noexcept { return itr; }
  };

  struct reviter {
    std::size_t itr;
    constexpr reviter(std::size_t pos) noexcept: itr(pos) { }
    constexpr void operator ++ () noexcept { --itr; }
    constexpr bool operator != (reviter other) const noexcept { return itr != other.itr; }
    constexpr std::size_t operator * () const noexcept { return itr; }
  };

  const iter first, last;

public:
  constexpr range(std::size_t first, std::size_t last) noexcept: first(first), last(std::max(first, last)) { }
  constexpr iter begin() const noexcept { return first; }
  constexpr iter end() const noexcept { return last; }
  constexpr reviter rbegin() const noexcept { return reviter(*last - 1); } 
  constexpr reviter rend() const noexcept { return reviter(*first - 1); } 
};

/**
 * @title Range
 */
#line 15 "main.cpp"

using i32 = std::int32_t;
using i64 = std::int64_t;
using u32 = std::uint32_t;
using u64 = std::uint64_t;
using isize = std::ptrdiff_t;
using usize = std::size_t;

constexpr i32 inf32 = (u32) ~0 >> 2;
constexpr i64 inf64 = (u64) ~0 >> 2;

template <class T>
using Vec = std::vector<T>;

int main() {
  usize N;
  u64 M, P;
  std::cin >> N >> M >> P;
  Vec<u64> A(N);
  for (auto &x: A) {
    std::cin >> x;
  }
  const auto Amax = *std::max_element(A.begin(), A.end());
  if (Amax > M) {
    std::cout << 1 << '\n';
    return 0;
  }
  auto B = A;
  for (auto &x: B) {
    while (x % P == 0) {
      x /= P;
    }
  }
  const auto Bmax = *std::max_element(B.begin(), B.end());
  if (Bmax == 1) {
    std::cout << -1 << '\n';
  }
  else {
    u64 cur = 1;
    usize ans = 0;
    while (cur * Amax <= M) {
      cur *= Bmax;
      ans += 1;
    }
    std::cout << ans + 1 << '\n';
  }
  return 0;
}