#include <bits/stdc++.h>
#define all(cont) cont.begin(), cont.end()
#define pb push_back
#define fi first
#define se second
#define DEBUG(x) cerr << (#x) << ": " << (x) << '\n'

using namespace std;

typedef pair<int, int> pii;
typedef vector<int> vi;
typedef long long ll;
typedef unsigned long long ull;

template<class T> bool uin(T &a, T b) {return (a < b ? false : (a = b, true));}
template<class T> bool uax(T &a, T b) {return (a > b ? false : (a = b, true));}

ifstream f("dreptpal.in");
ofstream g("dreptpal.out");

const int NMAX = 1005;

int stk[NMAX];
vector<int> v(NMAX);
vector<vector<int>> lps(NMAX, vector<int>(2 * NMAX));

void manacher(vector<int> &lps, int n) {
  int c = 1, r = 1;
  lps[1] = 1;
  for (int i = 2; i <= n; ++i) {
    int sim = 2 * c - i;
    if (i < r) {
      lps[i] = min(lps[sim], r - i);
    }
    int lft = i - lps[i];
    int rgt = i + lps[i];
    while (lft - 1 >= 1 && rgt + 1 <= n && v[lft - 1] == v[rgt + 1]) {
      ++lps[i];
      --lft;
      ++rgt;
    }
    if (i + lps[i] > r) {
      r = i + lps[i];
      c = i;
    }
  }
  for (int i = 2, j = 1; i <= n; i += 2, ++j) {
    lps[j] = lps[i];
  }
}

int solve(vector<int> &h, int n) {
  fill(stk, stk + n + 1, 0);
  int top = 0;
  int ret = 0;
  for (int i = 1; i <= n; ++i) {
    while (top && h[stk[top]] >= h[i]) {
      ret = max(ret, h[stk[top]] * (i - stk[top - 1] - 1));
      --top;
    }
    stk[++top] = i;
  }
  while (top) {
    ret = max(ret, h[stk[top]] * (n - stk[top - 1]));
    --top;
  }
  return ret;
}

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
#ifdef LOCAL_DEFINE
  freopen(".in", "r", stdin);
#endif

  int n, m;
  f >> n >> m;
  for (int i = 1; i <= n; ++i) {
    for (int j = 1; j <= 2 * m; ++j) {
      if (j & 1) {
        v[j] = -1;
      } else {
        f >> v[j];
      }
      v[2 * m + 1] = -1;
    }
    manacher(lps[i], 2 * m + 1);
  }

  int ans = 0;
  for (int i = 1; i <= m; ++i) {
    for (int j = 1; j <= n; ++j) {
      v[j] = lps[j][i];
    }
    ans = max(ans, solve(v, n));
  }

  g << ans << '\n';

  f.close();
  g.close();

#ifdef LOCAL_DEFINE
  cerr << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";
#endif
  return 0;
}