#include <bits/stdc++.h>   using namespace std;   const int maxn = 1e5 + 10, mod = 1e9 + 7, INF = 0x3f3f3f3f;   int main() {     int T;     cin >> T;     while (T--) {       int n, k;       cin >> n >> k;       int mn = INF, mx = -1;       for (int i = 1; i <= n; ++i) {         int x;         scanf( %d , &x);         mn = min(mn, x);         mx = max(mx, x);       }       int m = (mx + mn) >> 1;       printf( %d n , max(m - mn, mx - m) <= k ? mn + k : -1);     }     return 0;   }   