#include<stdio.h>
#include<algorithm>
using namespace std;

#define MaxN 1100
#define ll long long

int N,M,MAX = 0,A[MaxN][MaxN],B[MaxN][MaxN],C[MaxN],D[MaxN];

void citire(void)
{
	FILE *f = fopen("dreptpal.in","r");
	
	fscanf(f,"%d %d",&N,&M);
	for(int i=1;i<=N;i++)
		for(int j=1;j<=M;j++)
			fscanf(f,"%d ",&A[i][j]);
	
	fclose(f);
}

void Bb(void)
{
	int k = 0;
	for(int i=1;i<=N;i++)
		for(int j=1;j<=M;j++)
		{
			for(k = 1;A[i][j-k] == A[i][j+k] && j-k && j+k <= M;k++);
			B[i][j] = 1 + 2*(k-1);
		}
}

int cmp(int a,int b)
{
	return a > b;
}

void Max(void)
{
	int MIN,MIN2,l = 0;
	for(int i=1;i<=M;i++)
	{
		MIN2 = l = 0;
		for(int j=1;j<=N;j++)
			C[j] = D[j] = B[j][i];
		sort(D+1,D+N+1,cmp);
		for(int i=1;i<=N;i++)
			if(D[i] != D[i-1] && D[i] != 1)
			{
				int SUM = 0;
				for(int j=1;j<=N;j++)
					if(C[j] >= D[i])
						SUM += D[i], SUM > MAX ? MAX = SUM:0;
					else
						SUM = 0;
			}
	}
}

int main()
{
	FILE *g = fopen("dreptpal.out","w");
	
	citire();
	Bb();
	Max();
	fprintf(g,"%d ",MAX > N ? MAX:N);
	
	fclose(g);
	return 0;
}