C

#include <bits/stdc++.h>
#define LL long long

using namespace std;

int main()
{
    int t;
    cin>>t;
    while(t--)
    {

    int n;
    LL k;
    cin >> n;
    cin >> k;
    vector<LL>a_arr(n);
    for(int i=0;i<n;i++)
    {
        cin>>a_arr[i];
    }
    LL l=0,r=1e18;
    while(l<r)
    {
        LL mid=(l+r+1)/2;
        LL ans=mid+(n-1);
        LL need=0,t=0;
        for(int i=0;i<n;i++)
        {
            if(a_arr[i]>ans/n)
            {
                t++;
            }
            else
            {
                LL tmp = ans/n-a_arr[i];
                need += tmp;
            }
        }
        need+=max(ans%n-t,0ll);
        if(need<=k)l=mid;
        else r=mid-1;
    }
    cout<<l;
    cout << endl;
    }
}