#include <bits/stdc++.h>
using namespace std;
int a[410][410], f[410][410], ans, n, m;
unsigned short g[410][410 * 410];
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++) scanf("%d", &a[i][j]);
  for (int i = 1; i <= n; i++) {
    for (int l = m; l; l--)
      for (int r = l; r <= m; r++) {
        if (l == r)
          f[l][r] = max(f[l][r], (int)g[l][a[i][l]]);
        else {
          f[l][r] = max(f[l][r], max(f[l][r - 1], f[l + 1][r]));
          f[l][r] = max(f[l][r], (int)max(g[l][a[i][r]], g[r][a[i][l]]));
          if (a[i][l] == a[i][r]) f[l][r] = i;
        }
        ans = max(ans, (i - f[l][r]) * (r - l + 1));
      }
    for (int j = 1; j <= m; j++) g[j][a[i][j]] = i;
  }
  cout << ans << endl;
  return 0;
}
