#include<bits/stdc++.h>
// #include<atcoder/all>
// using namespace std;
// using namespace atcoder;
#define int long long
#define rep(i, n) for(int i = 0;i<(int)(n);i++)
#define all(v) (v).begin(),(v).end()
using ll = long long;
using lint = long long;
using P = std::pair<int,int>;

signed main(void) {
    int n,m,p;
    std::cin >> n >> m >> p;
    std::vector<int> v(n);
    int max = 0;
    rep(i, n) {
        std::cin >> v[i];
        max=std::max(max,v[i]);
        if(v[i]>m) return printf("1\n"),0;
        if(v[i]<=m&&v[i]%p==0) {
            while(v[i]%p==0) v[i]/=p;
        }
    }
    std::sort(v.rbegin(),v.rend());
    int ans = 1;
    if(v.front()==1) ans=-1;
    else {
        int x = 1;
        while(x*max<=m) x*=v.front(),ans++;
    }
    std::cout << ans << std::endl;
    return 0;
}