#include <bits/stdc++.h>
using namespace std;
const long long inf = 1e10;
long long s[300005];
int main() {
  int T;
  long long n, k;
  scanf("%d", &T);
  while (T--) {
    scanf("%lld %lld", &n, &k);
    for (long long i = 1; i <= n; i++) scanf("%lld\n", &s[i]);
    long long ans = inf, v;
    for (long long i = k + 1; i <= n; i++) {
      if (ans > (s[i] - s[i - k])) ans = s[i] - s[i - k], v = i;
    }
    long long kk = (s[v] + s[v - k]) / 2;
    cout << kk << endl;
  }
  return 0;
}
