5502.java

import java.io.*;
import java.util.*;

public class Main {

    static class Node{
        String str;
        int cnt;

        public Node(String str, int cnt) {
            this.str = str;
            this.cnt = cnt;
        }
    }

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
        StringTokenizer st = new StringTokenizer(br.readLine());

        int N = Integer.parseInt(st.nextToken());

        st = new StringTokenizer(br.readLine());

        StringBuilder sb = new StringBuilder();

        sb.append(st.nextToken());

        StringBuilder reverse = new StringBuilder(sb).reverse();

        int[][] dp = new int[N + 1][N + 1];

        for (int i = 1; i <= N; i++) {
            for (int j = 1; j <= N; j++) {
                if (sb.charAt(i - 1) == reverse.charAt(j - 1)) {
                    dp[i][j] = dp[i-1][j-1] + 1;
                } else{
                    dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
                }
            }
        }


        bw.write(N - dp[N][N]+"\n");

        bw.flush();
    }



}