#include <bits/stdc++.h>
using namespace std;
const int N = 401;
const int M = 160001;
const int K = 1e6 + 1;
short pos[M][N], max1[N][N];
int ar[N][N], val[K], sz = 0;
vector<int> lis;
signed main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n, i, j, k, l, m, cnt = 0, ans = 0;
  cin >> n >> m;
  for (i = 1; i <= n; i++) {
    for (j = 1; j <= m; j++) {
      cin >> ar[i][j];
      lis.push_back(ar[i][j]);
    }
  }
  sort(lis.begin(), lis.end());
  i = j = 0;
  while (i < lis.size()) {
    while (j < lis.size() && lis[i] == lis[j]) {
      j++;
    }
    sz++;
    val[lis[i]] = sz;
    i = j;
  }
  for (i = 1; i <= n; i++) {
    for (j = 1; j <= m; j++) {
      ar[i][j] = val[ar[i][j]];
    }
  }
  for (i = 1; i <= n; i++) {
    for (l = 1; l <= m; l++) {
      for (j = 1; j + l - 1 <= m; j++) {
        k = j + l - 1;
        if (j == k) {
          max1[j][k] = max(max1[j][k], pos[ar[i][j]][j]);
        } else {
          if (ar[i][j] == ar[i][k]) {
            max1[j][k] = i;
          } else {
            max1[j][k] =
                max(max1[j][k], max(max(max1[j + 1][k], pos[ar[i][k]][j]),
                                    max(max1[j][k - 1], pos[ar[i][j]][k])));
          }
        }
        ans = max(ans, l * (i - max1[j][k]));
      }
    }
    for (j = 1; j <= m; j++) {
      pos[ar[i][j]][j] = i;
    }
  }
  cout << ans;
}
