#pragma comment(linker, "/STACK:1024000000,1024000000")

#include <cstdio>

#include <string>

#include <cstdlib>

#include <cmath>

#include <iostream>

#include <cstring>

#include <set>

#include <queue>

#include <algorithm>

#include <vector>

#include <map>

#include <cctype>

#include <cmath>

#include <stack>

#include <sstream>

#include <unordered_map>

#include <unordered_set>

#define debug() puts("++++");

#define freopenr freopen("in.txt", "r", stdin)

#define freopenw freopen("out.txt", "w", stdout)

using namespace std;

typedef long long LL;

typedef unsigned long long ULL;

typedef pair<int, int> P;

const int INF = 0x3f3f3f3f;

const LL LNF = 1LL << 60;

const double inf = 0x3f3f3f3f3f3f;

const double PI = acos(-1.0);

const double eps = 1e-8;

const int maxn = 1000 + 5;

const int mod = 2000;

const int dr[] = {-1, 1, 0, 0};

const int dc[] = {0, 0, 1, -1};

const char *de[] = {"0000", "0001", "0010", "0011", "0100", "0101", "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101", "1110", "1111"};

int n, m;

const int mon[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

const int monn[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};

inline bool is_in(int r, int c){

    return r >= 0 && r < n && c >= 0 && c < m;

}

int dp[maxn][maxn];

char s[maxn];

int a[maxn];

bool vis[30];

int main(){

    int T;  cin >> T;

    while(T--){

        scanf("%d", &n);

        int cnt = 0;

        scanf("%s", s);

        int len = strlen(s);

        int t = len / n;

        memset(dp, INF, sizeof dp);

        memset(vis, false, sizeof vis);

        for(int i = 0; i < n; ++i)

            vis[s[i]-'a'] = true;

        for(int i = 0; i < 26; ++i)  if(vis[i])  ++cnt;

        for(int i = 0; i < n; ++i)  dp[0][i] = cnt;

        for(int i = 1; i < t; ++i){

            cnt = 0;

            memset(vis, false, sizeof vis);

            for(int j = i*n; j < (i+1)*n; ++j)

                vis[s[j]-'a'] = true;

            for(int j = 0; j < 26; ++j)  if(vis[j])  ++cnt;

            for(int j = 0; j < n; ++j){

                int fro = i * n + j;

                for(int k = 0; k < n; ++k){

                    int rear = (i-1) * n + k;

                    if(vis[s[rear]-'a'] && (1 == cnt || s[rear] != s[fro]))  dp[i][j] = min(dp[i][j], dp[i-1][k] + cnt - 1);

                    else   dp[i][j] = min(dp[i][j], dp[i-1][k] + cnt);

                }

            }

        }

        int ans = INF;

        for(int i = 0; i < n; ++i)  ans = min(ans, dp[t-1][i]);

        printf("%d\n", ans);

    }

    return 0;

}