#include <bits/stdc++.h>
using namespace std;
vector<vector<long long>> adj;
map<long, bool> vis, viss;
vector<long long> rnk, parent, sz;
int spf[1000000 + 1];
long long binpow(long long a, long long b, long long m) {
  a %= m;
  long long res = 1;
  while (b > 0) {
    if (b & 1) res = res * a % m;
    a = a * a % m;
    b >>= 1;
  }
  return res;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(nullptr);
  long long t, temp;
  long long n, k;
  cin >> t;
  while (t--) {
    cin >> n >> k;
    vector<long long> v;
    for (long long i = 0; i < n; i++) {
      cin >> temp;
      v.push_back(temp);
    }
    long long yg = k + 1;
    long long mn = LLONG_MAX;
    long long ans = -1;
    if (n == 1) {
      cout << v[0] << "\n";
      continue;
    }
    for (long long i = 0; i + yg - 1 < n; i++) {
      if (mn > (v[i - 1 + yg] - v[i] + 1) / 2) {
        mn = (v[i - 1 + yg] - v[i] + 1) / 2;
        ans = (v[i - 1 + yg] + v[i] + 1) / 2;
      };
    }
    cout << ans << "\n";
  }
  return 0;
}
