#include <bits/stdc++.h>   using namespace std;   int main() {     int n, m, min, max, i, t, f = 0;     cin >> n >> m;     cin >> min;     max = min;     for (i = 1; i < n; i++) {       cin >> t;       if (t > max)         max = t;       else if (t < min)         min = t;     }     if (2 * min > max) max = 2 * min;     for (i = 0; i < m; i++) {       cin >> t;       if (t <= max) f = 1;     }     if (f == 1)       cout <<  -1 n ;     else       cout << max << endl;     return 0;   }   