import java.util.Scanner;

public class Abb {
    public static void main(String[] args) {
        var sc = new Scanner(System.in);
        sc.nextLine();
        var arr = sc.nextLine().toCharArray();

        if(isPal(arr, 0, arr.length - 1) == -1){
            System.out.println(arr.length - 1);
            return;
        }

        int tmp;
        boolean cool = false;

        for (int i = 0; i < arr.length; i++) {
            if ((tmp = isPal(arr, i, arr.length - 1)) == -1) {
                System.out.println(i);
                cool = true;
                break;
            } else {
                i = tmp;
            }
        }
        if (!cool) System.out.println(arr.length - 1);
        // System.out.println(arr.length - 1);

    }

    public static int isPal(char[] arr, int a, int b) {
        int tmp = a;
        int end = b;
        for(; a < b; a++, b--) {
            if(arr[a] == arr[end]){
                tmp = a;
            }
            if (arr[a] != arr[b]) {
                return tmp;
            }
        }
        return -1;
    }
}