#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
using namespace __gnu_pbds;
using namespace std;
typedef long long ll;
typedef long double ld;
#define pb push_back
#define X first
#define Y second
#define sz(v) (int)v.size()
using ord = tree<int, null_type, greater<int>, rb_tree_tag, tree_order_statistics_node_update>;

void solve();

main() {
	ios_base::sync_with_stdio(0), cin.tie(0);
#ifdef ONPC
	freopen("in.txt", "r", stdin);
#endif
	int t = 1;
	cin >> t;
	while (t--) solve();
	return 0;
}

const int N = 2e5 + 5;
int n, k, a[N][30];
string s;

void solve() {
	cin >> n >> k >> s;
	for (int i = 0; i < k; ++i) {
		for (int j = 0; j < 30; ++j) {
			a[i][j] = 0;
		}
	}
	for (int i = 0; i < sz(s); ++i) {
		++a[i % k][s[i] - 'a'];
	}
	int del = n / k;
	int ans = 0;
	int lef = 0, rig = k - 1;
	while (lef <= rig) {
		int cur = 1e9 + 7;
		if (lef == rig) {
			for (int z = 0; z < 26; ++z) {
				cur = min(cur, del - a[lef][z]);
			}
		} else {
			for (int z = 0; z < 26; ++z) {
				cur = min(cur, del + del - a[lef][z] - a[rig][z]);
			}
		}
		ans += cur;
		++lef;
		--rig;
	}
	cout << ans << '\n';
}