#ifndef ONLINE_JUDGE
#define _GLIBCXX_DEBUG
#endif
#include<bits/stdc++.h>
using namespace std;
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
#define bit(n,k) (((ll)n>>(ll)k)&1) /*nのk bit目*/
#define pb push_back
#define pf push_front
#define FI first
#define SE second
#define eb emplace_back
#define endl '\n'
#define SZ(x) ((ll)(x).size())
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define PI 3.14159265359
const double eps = 1e-12;
const long long INF= 1e+18+1;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vector<ll> >vvl;
typedef vector<vector<vector<ll> > >vvvl;
typedef vector<vector<vector<vector<ll> > > >vvvvl;
typedef vector<vector<vector<vector<vector<ll> > > > >vvvvvl;
typedef pair<ll,ll> P;
typedef tuple<ll,ll,ll> T;
typedef struct Point_Coordinates {
    ll x, y;
} point;
template<class T> using minpq=priority_queue<T,vector<T>,greater<T>>;
const ll MOD=1000000007LL;
//ll MOD=1000000007LL;
// const ll MOD=998244353LL;
//const ll MOD=1777777777LL;
//const ll MAX_V=114514LL;
//const ll MAX = 500010LL;
const ll mod=MOD;
string abc="abcdefghijklmnopqrstuvwxyz";
string ABC="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
vl dx={0,0,1,-1,1,1,-1,-1};
vl dy={1,-1,0,0,-1,1,-1,1};


template<class T>bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>bool chmin(T &a,const T &b){if(b<a){a=b;return true;}return false;}
 
struct IOSetup{
    IOSetup(){
        cin.tie(0);
        ios::sync_with_stdio(0);
        cout<<fixed<<setprecision(12);
    }
} iosetup;
 
template<typename T>
ostream &operator<<(ostream &os,const vector<T>&v){
    for(int i=0;i<(int)v.size();i++) os<<v[i]<<(i+1==(int)v.size()?"":" ");
    return os;
}
template<typename T>
istream &operator>>(istream &is,vector<T>&v){
    for(T &x:v)is>>x;
    return is;
}
 
// 2^127 = 170141183460469231731687303715884105728 ~ 10^38
using int128=__int128;
 
ostream &operator<<(ostream &os,const __int128 n){
    if(n==0){
        os<<0;
        return os;
    }
    __int128 num=n;
    bool neg=false;
    if(num<0)neg=true,num=-num;
    string res="";
    while(num>0){
        res.push_back('0'+num%10);
        num/=10;
    }
    if(neg) res.push_back('-');
    reverse(begin(res),end(res));
    os<<res;
    return os;
}
 
istream &operator>>(istream &is,__int128 &n){
    string s;
    is>>s;
    int idx=0;
    bool neg=false;
    if(s[0]=='-')neg=true,idx++;
    n=0;
    for(;idx<(int)s.size();idx++){
        n=10*n+s[idx]-'0';
    }
    if(neg) n=-n;
    return is;
}
 
__int128 abs128(__int128 x){
    return x<0?-x:x;
}
 
__int128 gcd128(__int128 a,__int128 b){
    if(a==0) return b;
    if(b==0) return a;
    return b>0?gcd128(b,a%b):a;
}

namespace fastprime{
    int128 pow_mod(int128 a,int128 n,int128 m){
        int128 ret=1;
        while(n){
            if(n&1)ret=ret*a%m;
            a=a*a%m;
            n>>=1;
        }
        return ret;
    }
 
    bool miller_rabin(int128 n){
        if(n<=1) return false;
        if(n==2) return true;
        if(n%2==0) return false;
        int128 d=n-1,s=0;
        while(!(d&1))d>>=1,s++;// n-1=2^s*d
        for(int128 a:{2,3,5,7,11,13,17,19,23,29,31,37}){
            if(n<=a) break;
            int128 y=pow_mod(a,d,n);// y=a^d (mod n)
            int128 t;
            for(t=d;t<n-1 and y!=1 and y!=n-1;t<<=1) y=y*y%n;
            if(y!=n-1 and t%2==0) return false;
        }
        return true;
    }
 
    int128 pollard_rho_single(int128 n){
        auto f=[&](int128 x){return (x*x+1)%n;};
        if(miller_rabin(n)) return n;
        if(!(n&1)) return 2;
        int128 a=0;
        while(true){
            a++;
            int128 x=a;
            int128 y=f(x);
            while(true){
                int128 g=gcd128(y-x+n,n);
                if(g==0 or g==n) break;
                if(g!=1) return g;
                x=f(x);
                y=f(f(y));
            }
        }
    }
 
    vector<int128> pollard_rho(int128 n){
        if(n==1) return {};
        int128 x=pollard_rho_single(n);
        if(x==n) return {x};
        vector<int128> l=pollard_rho(x);
        vector<int128> r=pollard_rho(n/x);
        l.insert(l.end(),r.begin(),r.end());
        return l;
    }
}

#define ll int128
#define int int128



signed main(){
    int n;
    ll m;
    int p;
    cin>>n>>m>>p;
    vector<ll> a(n);
    rep(i,n)cin>>a[i];      
    ll now=1;
    ll ma=1;
    rep(i,n){
        if(a[i]%p!=0)chmax(now,a[i]);
        else chmax(now,a[i]/p);
        chmax(ma,a[i]);
    }
    if(now==1){
        if(ma>m){
            cout<<1<<endl;
        }
        else{
            cout<<-1<<endl;
        }
        return 0;
    }
    ll cnt=0;
    ll cur=1;
    while(cur*ma<=m){
        cur*=now;
        cnt++;
    }
    cout<<cnt+1<<endl;

}