#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
using namespace std;
int n, m, a[410][410], ans;
int last[1000010];
int L[410][410], R[410][410], limit[410];
int main() {
  ios_base ::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> m;
  for (int i = 1; i <= n; ++i)
    for (int j = 1; j <= m; ++j) cin >> a[i][j];
  for (int up = n; up >= 1; --up) {
    for (int i = 1; i <= m; ++i) {
      if (last[a[up][i]])
        L[up][i] = last[a[up][i]];
      else
        L[up][i] = 0;
      last[a[up][i]] = i;
      for (int down = up + 1; down <= n; ++down)
        if (last[a[down][i]] && L[down][i] < last[a[down][i]])
          L[down][i] = last[a[down][i]];
    }
    for (int i = 1; i <= m; ++i) last[a[up][i]] = 0;
    for (int i = m; i >= 1; --i) {
      if (last[a[up][i]])
        R[up][i] = last[a[up][i]];
      else
        R[up][i] = m + 1;
      last[a[up][i]] = i;
      for (int down = up + 1; down <= n; ++down)
        if (last[a[down][i]] && R[down][i] > last[a[down][i]])
          R[down][i] = last[a[down][i]];
    }
    for (int i = 1; i <= m; ++i) last[a[up][i]] = 0;
    for (int i = 1; i <= m + 1; ++i) limit[i] = m + 1;
    for (int down = up; down <= n; ++down) {
      for (int i = m; i >= 1; --i) {
        if (limit[i] > limit[i + 1]) limit[i] = limit[i + 1];
        if (limit[i] > R[down][i]) limit[i] = R[down][i];
        if (limit[L[down][i]] > i) limit[L[down][i]] = i;
        if ((limit[i] - i) * (down - up + 1) > ans)
          ans = (limit[i] - i) * (down - up + 1);
      }
    }
  }
  cout << ans;
}
