codeforce - Equalize Prices

#include<bits/stdc++.h>
using namespace std;
#define fast()(ios_base::sync_with_stdio(0),cin.tie(NULL));
int main()
{
    int q;
    fast();
    cin>>q;
    while(q--)
    {
        int n,k;
        cin>>n>>k;
        int ara[n+1],mn,mx=0;
        for(int i=0;i<n;i++)
        {
            cin>>ara[i];
            if(ara[i]>mx)mx=ara[i];
            if(ara[i]<mn)mn=ara[i];
            if(i==0)mn=ara[i];
        }
        //cout<<mn<<mx<<endl;
        int x=mx-mn;
        if(x%2==0)x=x/2;
        else x=(x/2)+1;
        if(x>k)cout<<"-1"<<endl;
        else
        {
            int ans=max(mn+k,mx-x);
            cout<<ans<<endl;
        }
    }
}