#include <bits/stdc++.h>
using namespace std;
template <class T>
T sqr(T x) {
  return x * x;
}
const int maxn = 401;
short f[maxn][maxn][maxn];
int a[maxn][maxn];
int vis[160001];
short plc[160001];
int n, m;
inline short min(short a, short b) {
  if (a < b) return a;
  return b;
}
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++) scanf("%d", &a[i][j]);
  int now = 0;
  int ans = 0;
  for (int d = 1; d <= n; d++)
    for (int i = 1; i + d - 1 <= n; i++) {
      int j = i + d - 1;
      now++;
      for (int k = m; k >= 1; k--) {
        f[i][j][k] = m;
        if (k < m) f[i][j][k] = f[i][j][k + 1];
        if (i < j) {
          f[i][j][k] = min(f[i][j][k], f[i + 1][j][k]);
          f[i][j][k] = min(f[i][j][k], f[i][j - 1][k]);
        }
        if (i < j && a[i][k] == a[j][k]) f[i][j][k] = k - 1;
        if (vis[a[i][k]] == now)
          f[i][j][k] = min(f[i][j][k], (short)plc[a[i][k]] - 1);
        if (vis[a[j][k]] == now)
          f[i][j][k] = min(f[i][j][k], (short)plc[a[j][k]] - 1);
        vis[a[i][k]] = now;
        vis[a[j][k]] = now;
        plc[a[i][k]] = k;
        plc[a[j][k]] = k;
        ans = max(ans, d * (f[i][j][k] - k + 1));
      }
    }
  cout << ans << endl;
}
