#include <fstream>

const int NMMAX = 1005;

using namespace std;
ifstream f("dreptpal.in");
ofstream g("dreptpal.out");

int N,M,A[NMMAX][NMMAX],Pal[NMMAX][NMMAX],cont,it,Stack[NMMAX],SOL;

int minim(int a, int b)
{
    if (a < b)
        return a;
    return b;
}

int maxim(int a, int b)
{
    if (a > b)
        return a;
    return b;
}

void Solve(int ii, int jj)
{
    int top = 1,maxx;
    maxx = Pal[ii][jj];
    Stack[top] = Pal[ii][jj];
    for (int i = ii; i >= 1; i--)
    {
        top++;
        if (Pal[i][jj])
        {
            Stack[top] = minim(Stack[top-1],Pal[i][jj]);
            maxx = maxim(maxx,top*Stack[top]);
        }
    }
    SOL = maxim(SOL,maxx);
}

int main()
{
    f >> N >> M;
    for (int i = 1; i <= N; ++i)
    {
        for (int j = 1; j <= M; ++j)
        {
            f >> A[i][j];
        }
    }
    for (int i = 1; i <= N; ++i)
    {
        for (int j = 2; j < M; ++j)
        {
            cont = 1;
            it = 1;
            while (j-it >=1 && j + it <= M && A[i][j-it] == A[i][j+it])
            {
                Pal[i][j] = cont;
                cont++;
                it++;
            }
        }
    }

    for (int i = 1; i <= N; ++i)
    {
        for (int j = 1; j <= M; ++j)
        {
            if (Pal[i][j] != 0)
                Solve(i,j);
        }
    }

    g << SOL*2+1;

    f.close();
    g.close();
    return 0;
}