#include <iostream>
#include <algorithm>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <numeric>
#include <bitset>
#include <cmath>

static const int MOD = 1000000007;
using ll = long long;
using u32 = unsigned;
using u64 = unsigned long long;
using namespace std;

template<class T> constexpr T INF = ::numeric_limits<T>::max() / 32 * 15 + 208;

int main() {
    int n, m, p;
    cin >> n >> m >> p;
    vector<int> a(n);
    for (auto &&i : a) {
        scanf("%d", &i);
        while(i%p == 0) i /= p;
    }
    auto x = *max_element(a.begin(),a.end());
    if(x == 1) {
        puts("-1");
        return 0;
    }
    ll val = 1, ans = 0;
    while(val <= m) val *= x, ans++;
    cout << ans << "\n";
    return 0;
}