#include <iostream>
#include<stdio.h>

using namespace std;

int main() {
    FILE *fin, *fout;
    int i, max, n, s, elem;

    fin=fopen("loto.in", "r");
    fout=fopen("loto.out", "w");
    fscanf( fin, "%d %d", &n, &s);
    max=0;
    for(i=1;i<=n;i++) {
            fscanf( fin, "%d", &elem);
    if(elem>max) {
            max=elem;
    }
    if(max*6<s) {
            fprintf( fout, "-1");
    }
    }
    fclose( fin );
    fclose( fout );
    return 0;
}