#include <fstream>
using namespace std;
ifstream fin("loto.in");
ofstream fout("loto.out");
int v[100],n,s;
int main(){
 fin>>n>>s;
 for(int i=1;i<=n;i++){fin>>v[i];}
 sort(v+1,v+n+1);
 if(v[n]*6<s){fout<<"-1";return 0;}
 if(v[1]*6>s){fout<<"-1";return 0;}

 return 0;
}