#include <bits/stdc++.h>
using namespace std;
void getint(int &v) {
  char ch, fu = 0;
  for (ch = '*'; (ch < '0' || ch > '9') && ch != '-'; ch = getchar())
    ;
  if (ch == '-') fu = 1, ch = getchar();
  for (v = 0; ch >= '0' && ch <= '9'; ch = getchar()) v = v * 10 + ch - '0';
  if (fu) v = -v;
}
int n, m, ans, a[444][444], f[444][444], p[401][160001];
int main() {
  cin >> n >> m;
  for (int i = 1; i <= n; ++i)
    for (int j = 1; j <= m; ++j) getint(a[i][j]);
  for (int i = 1; i <= n; ++i) {
    for (int len = 1; len <= m; ++len)
      for (int l = 1; l <= m - len + 1; ++l) {
        int r = l + len - 1;
        if (len > 1) {
          f[l][r] = max(f[l][r], max(f[l + 1][r], f[l][r - 1]));
          f[l][r] = max(f[l][r], p[r][a[i][l]]);
          f[l][r] = max(f[l][r], p[l][a[i][r]]);
          if (a[i][l] == a[i][r]) f[l][r] = i;
        } else {
          f[l][r] = max(f[l][r], p[l][a[i][l]]);
        }
        ans = max(ans, (i - f[l][r]) * (r - l + 1));
      }
    for (int j = 1; j <= m; ++j) p[j][a[i][j]] = i;
  }
  cout << ans << endl;
  return 0;
}
