#include <fstream>
#include <vector>
#include <bitset>

using namespace std;

const char infile[] = "dreptpal.in";
const char outfile[] = "dreptpal.out";

ifstream fin(infile);
ofstream fout(outfile);

const int MAXN = 1005;
const int oo = 0x3f3f3f3f;

typedef vector<int> Graph[MAXN];
typedef vector<int> :: iterator It;

const inline int min(const int &a, const int &b) { if( a > b ) return b;   return a; }
const inline int max(const int &a, const int &b) { if( a < b ) return b;   return a; }
const inline void Get_min(int &a, const int b)    { if( a > b ) a = b; }
const inline void Get_max(int &a, const int b)    { if( a < b ) a = b; }

int A[MAXN][MAXN], N, M, dp[MAXN][MAXN], Stack[MAXN];

inline void buildManacher(int *p, int *DP) {
    int ind = 0, best = 0;
    for(int i = 1 ; i <= M ; ++ i) {
        if(best >= i)
            DP[i] = min(best - i, DP[2*ind - 1]);
        while(i - DP[i] - 1 >= 0 && i + DP[i] + 1 <= M && p[i - DP[i] - 1] == p[i + DP[i] + 1])
            ++DP[i];
        if(i + DP[i] > best) {
            best = i + DP[i];
            ind = i;
        }
    }
}

inline void Solve(void) {
    #ifdef debug
    for(int i = 1 ; i <= N ; ++ i, fout << '\n')
        for(int j = 1 ; j <= M ; ++ j)
            fout << A[i][j] << ' ';
    fout << "\n";
    for(int i = 1 ; i <= N ; ++ i, fout << '\n')
        for(int j = 1 ; j <= M ; ++ j)
            fout << dp[i][j] << ' ';
    #endif
    int Ans = 0;
    for(int j = 1; j <= M ; ++ j) {
        int top = 0;
        for(int i = 1 ; i <= N + 1 ; ++ i) {
            while( top > 0 && dp[i][j] <= dp[Stack[top]][j]) {
                int left = Stack[top - 1] + 1;
                int right = i - 1;
                Ans = max(Ans, (2*dp[Stack[top]][j] + 1) * (right - left + 1));
                -- top;
            }
            Stack[++ top] = i;
        }
    }
    fout << Ans << '\n';
}

int main() {
    fin >> N >> M;
    for(int i = 1 ; i <= N ; ++ i)
        for(int j = 1 ; j <= M ; ++ j)
            fin >> A[i][j];
    for(int i = 1 ; i <= N ; ++ i)
        buildManacher(A[i], dp[i]);
    Solve();
    fin.close();
    fout.close();
    return 0;
}