import java.io.*;

public class LargesAreaInMatrix {
    public static void main(String[] args) throws Exception {
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        String[] tokens = in.readLine().split(" ");
        int a = Integer.parseInt(tokens[0]);
        int b = Integer.parseInt(tokens[1]);
		int[][] array=new int[a][b];
		for(int i=0;i<a;i++){
			String[] numbers = in.readLine().split(" ");
			for(int j=0;j<b;j++){
				array[i][j]=Integer.parseInt(numbers[j]);
			}
		}
		int maxSum[][]=new int[1024][1];
		for(int i=0;i<1024;i++){
			maxSum[i][0]=Integer.MIN_VALUE;
		}
		int currentSum[][]=new int[1024][1];
		for(int i=1;i<a-1;i++){
			for(int j=1;j<b-1;j++){
				int aray=array[i][j];
				currentSum[aray][0]+=neighbours(array,i,j);
				if(maxSum[aray][0]<=currentSum[aray][0]){
					maxSum[aray][0]=currentSum[aray][0];
				}
			}
		}
		int maxxSum=Integer.MIN_VALUE;
		for(int i=0;i<1024;i++){
			if(maxxSum<=maxSum[i][0]){
				maxxSum=maxSum[i][0];
			}
		}
		System.out.println(maxxSum);
    }
	public static int neighbours(int[][] arraySum,int row,int col){
		int sum=0;
		if(arraySum[row][col]==arraySum[row+1][col]){
			sum++;
		}
		if(arraySum[row][col]==arraySum[row][col+1]){
			sum++;
		}
		if(arraySum[row][col]==arraySum[row-1][col]){
			sum++;
		}
		if(arraySum[row][col]==arraySum[row][col-1]){
			sum++;
		}
		return sum;
	}

}