nombre ennemis matrice touchés explosion

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

/**
 * Auto-generated code below aims at helping you parse
 * the standard input according to the problem statement.
 **/
class Solution {

    public static void main(String args[]) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int m = in.nextInt();
        List<Integer> enemies = new ArrayList<>();
        char[][] mat = new char[m][m];
        if (in.hasNextLine()) {
            in.nextLine();
        }
        for (int i = 0; i < m; i++) {
            String battleground = in.nextLine();
            for(int j = 0; j < m; j++)
                mat[i][j] = battleground.charAt(j);
        }
        if(m <= n)
            System.out.println(numberOfX(mat,m));
            else
            {
        for(int i = 0; i <= m - n; i++)
        {
            for(int j = 0; j <= m - n; j++)
                enemies.add(numberEnemiesInSquare(mat,i,j,n));
        }
        int max = 0;
        for(int x : enemies)
            if(x > max)
                max = x;
        System.out.println(max);
            }

    }
    public static int numberEnemiesInSquare(char[][] mat,int x, int y, int size)
    {
        int enemies = 0;
        for(int i = x; i < x + size; i++)
            for(int j = y; j < y + size; j++)
                if(mat[i][j] == 'x')
                    enemies++;
        return enemies;
    }
    public static int numberOfX(char[][] mat,int size)
    {
        /* plutôt
    return numberEnemiesInSquare(mat, 0, 0, size);
        */
        int total = 0;
        for(int i = 0; i <  size; i++)
            for(int j = 0; j < size; j++)
                if(mat[i][j] == 'x')
                    total++;
                    return total;
    }
}