Codeforces Round #570 (Div. 3) B. Equalize Prices

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<cstring>
#include<set>
#define ll long long
using namespace std;
const int maxn = 200010;
const int inf = 0x3f3f3f3f;
int main()
{
    int t;
    cin >> t;
    while (t--)
    {
        int n, q;
        cin >> n >> q;
        int a[110];
        for (int i = 0; i < n; i++)
        {
            cin >> a[i];
        }
        sort(a, a + n);
        int contrast = a[n - 1] - a[0];
        if (contrast > 2 * q)
        {
            printf("-1\n");
        }
        else
        {
            printf("%d\n", a[0] + q);
        }
    }
}