#include <bits/stdc++.h>
using namespace std;
const int maxn = 405;
int a[maxn][maxn], d[maxn][maxn], f[maxn][maxn], n, m, i, t, j, k, l, r, x, y,
    z, p[maxn][maxn * maxn], mx, ans;
int main() {
  scanf("%d%d", &n, &m);
  for (i = 1; i <= n; i++)
    for (j = 1; j <= m; j++) scanf("%d", &a[i][j]);
  for (j = 1; j <= m; j++) {
    for (l = n; l >= 1; l--)
      for (r = l; r <= n; r++) {
        f[l][r] = max(f[l][r - 1],
                      max(f[l + 1][r], max(p[l][a[r][j]], p[r][a[l][j]])));
        if (a[r][j] == a[l][j] && l != r) f[l][r] = j;
        d[l][r] = max(d[l][r], f[l][r]);
        ans = max(ans, (r - l + 1) * (j - d[l][r]));
      }
    for (i = 1; i <= n; i++) p[i][a[i][j]] = j;
  }
  printf("%d\n", ans);
}
