#include <bits/stdc++.h>
using namespace std;
int a[409][409], dp[409][409];
unsigned short last[409][160009];
int main() {
  int i, j, t1, t2, t3, t4, n, m, ans, l, r;
  scanf("%d %d", &n, &m);
  for (i = 1; i <= n; i++) {
    for (j = 1; j <= m; j++) {
      scanf("%d", &a[i][j]);
    }
  }
  ans = 1;
  for (i = 1; i <= n; i++) {
    for (l = m; l >= 1; l--) {
      for (r = l; r <= m; r++) {
        if (l == r) {
          dp[l][r] = max(dp[l][r], (int)last[l][a[i][l]]);
        } else {
          if (a[i][l] == a[i][r]) {
            dp[l][r] = max(dp[l][r], i);
          }
          dp[l][r] = max(dp[l][r], max(dp[l + 1][r], (int)last[l][a[i][l]]));
          dp[l][r] = max(dp[l][r], max(dp[l][r - 1], (int)last[r][a[i][r]]));
          dp[l][r] =
              max(dp[l][r], max((int)last[l][a[i][r]], (int)last[r][a[i][l]]));
        }
        ans = max(ans, (r - l + 1) * (i - dp[l][r]));
      }
    }
    for (j = 1; j <= m; j++) {
      last[j][a[i][j]] = i;
    }
  }
  printf("%d\n", ans);
  return 0;
}
