#include <bits/stdc++.h>
using namespace std;
#pragma GCC target("avx2")
#pragma GCC optimization("unroll-loops")
#pragma GCC optimize("O2")
constexpr int dx[] = {-1, 0, 1, 0, 1, 1, -1, -1};
constexpr int dy[] = {0, -1, 0, 1, 1, -1, 1, -1};
constexpr long long INF = 1999999999999999997;
constexpr int inf = INT_MAX;
constexpr int MAXSIZE = int(1e6) + 5;
constexpr auto PI = 3.14159265358979323846L;
constexpr auto oo = numeric_limits<int>::max() / 2 - 2;
constexpr auto eps = 1e-6;
constexpr auto mod = 1000000007;
constexpr auto MOD = 1000000007;
constexpr auto MOD9 = 1000000009;
constexpr auto maxn = 100006;
void fastio() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
}
int main() {
  fastio();
  int t;
  cin >> t;
  while (t--) {
    int n, k;
    cin >> n >> k;
    string s;
    cin >> s;
    int l = n / k;
    int a[k][26];
    memset(a, 0, sizeof(a));
    for (int i = 0; i < n; i++) {
      a[i % k][s[i] - 'a']++;
    }
    int ans = 0;
    for (int i = 0, p = k - 1; i < k, p >= 0; i++, p--) {
      int mn = 0;
      for (int j = 0; j < 26; j++) {
        mn = max(mn, a[i][j] + a[p][j]);
      }
      ans += (2 * l - mn);
    }
    cout << ans / 2 << "\n";
  }
}
