#include<bits/stdc++.h>
using namespace std;
using LL=long long;
using ULL=unsigned long long;
#define rep(i,n) for(int i=0; i<(n); i++)

ULL N,M,P;
ULL maxA,maxB;

int main(){
	scanf("%llu%llu%llu",&N,&M,&P);
	maxA=1; maxB=1;
	rep(i,N){
		ULL a; scanf("%llu",&a);
		maxA=max(maxA,a);
		while(a%P==0) a/=P;
		maxB=max(maxB,a);
	}
	ULL x=1;
	if(maxA>M){ printf("1\n"); return 0; }
	if(maxB==1){ printf("-1\n"); return 0; }
	ULL ans=1;
	while(x*maxA<=M){ x*=maxB; ans++; }
	printf("%llu\n",ans);
	return 0;
}