#include <bits/stdc++.h>
using namespace std;
#define int              long long int
#define double           long double
#define print(a)         for(auto x : a) cout << x << " "; cout << endl


const int M = 1000000007;
const int N = 3e5+9;
const int INF = 2e9+1;
const int LINF = 2000000000000000001;

inline int power(int a, int b) {
    int x = 1;
    a %= M;
    while (b) {
        if (b & 1) x = (x * a) % M; 
        a = (a * a) % M;
        b >>= 1;
    }
    return x;
}


//_ ***************************** START Below *******************************




string a;

int consistency(int n, int k){

    int l = (k-1)/2;
    int r = k/2;

    int ans = 0;

    int rows = n/k;

    while(l>=0 && r<k){
        vector<int> leftCol(26, 0);
        for(int i=l; i<n; i+=k){
            leftCol[a[i]-'a']++;
        }
        vector<int> rightCol(26, 0);
        for(int j=r; j<n; j+=k){
            rightCol[a[j]-'a']++;
        }

        int maxiF = 0;
        for(int i=0; i<26; i++){
            int targetF = leftCol[i] + rightCol[i];
            maxiF = max(maxiF, targetF);
        }

        int cost = (2*rows - maxiF);
        if(l==r) ans += cost/2;
        else ans += cost;


        l--;
        r++;
    }

    return ans;
}















int practice(int n, int k){


    return 0;
}





void solve() {
    
    int n, k;
    cin>> n >> k;
    cin >> a;
    
    
    cout << consistency(n, k) << endl;


}





int32_t main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    int t = 1;
    cin >> t;
    while (t--) {
        solve();
    }

    return 0;
}