#include <bits/stdc++.h>
using namespace std;
void __print(int x) { cout << x; }
void __print(long long x) { cout << x; }
void __print(double x) { cout << x; }
void __print(long double x) { cout << x; }
void __print(char x) { cout << '\'' << x << '\''; }
void __print(const string &x) { cout << '\"' << x << '\"'; }
void __print(bool x) { cout << (x ? "true" : "false"); }
template <typename T, typename V>
void __print(const pair<T, V> &x) {
  cout << '{';
  __print(x.first);
  cout << ',';
  __print(x.second);
  cout << '}';
}
template <typename T>
void __print(const T &x) {
  int f = 0;
  cout << '{';
  for (auto &i : x) cout << (f++ ? "," : ""), __print(i);
  cout << "}";
}
void _print() { cout << "]\n"; }
template <typename T, typename... V>
void _print(T t, V... v) {
  __print(t);
  if (sizeof...(v)) cout << ", ";
  _print(v...);
}
const int len = 2e5;
int cnt[len][26];
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int t;
  cin >> t;
  while (t--) {
    int n, k;
    cin >> n >> k;
    int m = n / k;
    for (int i = 0; i < k; i++) {
      for (int j = 0; j < 26; j++) cnt[i][j] = 0;
    }
    for (int i = 0; i < m; i++) {
      for (int j = 0; j < k; j++) {
        char c;
        cin >> c;
        cnt[j][c - 97]++;
      }
    }
    int ans = 0;
    int l = 0, r = k - 1;
    while (l <= r) {
      int mx = 0;
      for (int i = 0; i < 26; i++) mx = max(mx, cnt[l][i] + cnt[r][i]);
      if (l != r)
        ans += 2 * m - mx;
      else
        ans += m - mx / 2;
      l++, r--;
    }
    cout << ans << '\n';
  }
  return 0;
}
