#include <bits/stdc++.h>
using namespace std;
int n, m, a[401][401];
short int dp[401][401][401], u[401][401][401], v[160001];
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]);
  memset(dp, 0, sizeof(dp));
  memset(u, 0, sizeof(u));
  memset(v, 0, sizeof(v));
  for (int i = 1; i <= m; i++) {
    int l = n + 1;
    for (int j = n; j >= 1; j--) {
      while (!v[a[l - 1][i]] && l >= 2) {
        v[a[l - 1][i]] = 1;
        l--;
      }
      u[i][i][j] = l;
      v[a[j][i]] = 0;
    }
  }
  for (int i = 1; i <= m; i++)
    for (int j = i + 1; j <= m; j++) {
      int l = n + 1;
      for (int k = n; k >= 1; k--) {
        l = min(l, k + 1);
        while (!v[a[l - 1][i]] && !v[a[l - 1][j]] && l >= 2) {
          if (a[l - 1][i] == a[l - 1][j]) break;
          v[a[l - 1][i]] = v[a[l - 1][j]] = 1;
          l--;
        }
        u[i][j][k] = l;
        v[a[k][i]] = v[a[k][j]] = 0;
      }
    }
  for (int i = 1; i <= m; i++)
    for (int j = 1; j <= n; j++) dp[i][i][j] = u[i][i][j];
  for (int l = 2; l <= m; l++)
    for (int i = 1; i + l - 1 <= m; i++) {
      int j = i + l - 1;
      for (int k = 1; k <= n; k++)
        dp[i][j][k] = (short int)max(
            (short int)((short int)max((short int)(dp[i + 1][j][k]),
                                       (short int)(dp[i][j - 1][k]))),
            (short int)(u[i][j][k]));
    }
  int ans = 0;
  for (int i = 1; i <= m; i++)
    for (int j = i; j <= m; j++)
      for (int k = 1; k <= n; k++)
        ans = max(ans, int(k - dp[i][j][k] + 1) * int(j - i + 1));
  printf("%d\n", ans);
  return 0;
}
