#include <bits/stdc++.h>
using namespace std;
const int maxn = 412;
const int maxa = 161234;
int n, m;
int a[maxn][maxn], f[maxn][maxn], last[maxn][maxa];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cin >> n >> m;
  for (int(i) = (1); (i) <= (n); (i)++)
    for (int(j) = (1); (j) <= (m); (j)++) cin >> a[i][j];
  int ans = 0;
  for (int(i) = (1); (i) <= (n); (i)++)
    for (int(j) = (1); (j) <= (m); (j)++) {
      for (int(r) = (j); (r) <= (m); (r)++) {
        int l = r - j + 1;
        if (l == r)
          f[l][l] = max(f[l][l], last[l][a[i][l]]);
        else if (a[i][l] == a[i][r])
          f[l][r] = i;
        else
          f[l][r] = max({f[l][r], f[l][r - 1], f[l + 1][r], last[r][a[i][l]],
                         last[l][a[i][r]]});
        ans = max(ans, (i - f[l][r]) * (r - l + 1));
      }
      for (int(k) = (1); (k) <= (m); (k)++) last[k][a[i][k]] = i;
    }
  cout << ans;
}
