#include <bits/stdc++.h>
using namespace std;
const int maxn = 405, maxa = maxn * maxn;
int a[maxn][maxn], n, m, s[maxn][maxn], res, dau2[maxa], s2[maxn][maxn];
short int dau[maxn][maxa];
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; i++)
    for (int j = 0; j < m; j++) scanf("%d", &a[i][j]);
  for (int i = 0; i < m; i++)
    for (int j = 0; j < maxa; j++) dau[i][j] = -1;
  for (int j = 0; j < m + 1; j++)
    for (int l = 0; l < m + 1; l++) s[j][l] = -1;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++)
      for (int k = 0; k < m; k++) s2[j][k] = 0;
    for (int l = 0; l < m; l++) {
      for (int j = 0; j < m - l; j++) {
        int k = j + l;
        s2[j][k] = s2[j + 1][k] | (k > 0 ? s2[j][k - 1] : 0) |
                   (a[i][j] == a[i][k] && j != k);
        s[j][k] = max(s[j][k], max((k > 0 ? s[j][k - 1] : -1), s[j + 1][k]));
        s[j][k] = max(s[j][k], 0 + dau[k][a[i][j]]);
        s[j][k] = max(s[j][k], 0 + dau[j][a[i][k]]);
        if (s2[j][k] == 1) s[j][k] = i;
        if (s2[j][k] == 0) res = max(res, (k - j + 1) * (i - s[j][k]));
        if (i == 9 && j == 4 && k == 7) cout << "";
      }
    }
    for (int j = 0; j < m; j++) dau[j][a[i][j]] = i;
  }
  cout << res;
}
