#include <bits/stdc++.h>
using namespace std;
int N, M;
int A[402][402];
int cango[402], last[402 * 402];
int lf[402][402], rg[402][402];
int ST[402], result;
int main() {
  cin.sync_with_stdio(false);
  cin >> N >> M;
  for (int i = 1; i <= N; ++i)
    for (int j = 1; j <= M; ++j) cin >> A[i][j];
  for (int i = 1; i <= N; ++i)
    for (int j = 1; j <= M; ++j) rg[i][j] = M + 1;
  for (int i1 = N; i1 >= 1; --i1) {
    memset(last, 0, sizeof(last));
    for (int j = 1; j <= M; ++j) {
      for (int k = i1; k <= N; ++k) {
        if (last[A[k][j]] != 0) lf[k][j] = max(lf[k][j], last[A[k][j]]);
        if (k == i1) last[A[i1][j]] = j;
      }
    }
    memset(last, 0, sizeof(last));
    for (int j = M; j >= 1; --j) {
      for (int k = i1; k <= N; ++k) {
        if (last[A[k][j]] != 0) rg[k][j] = min(rg[k][j], last[A[k][j]]);
        if (k == i1) last[A[i1][j]] = j;
      }
    }
    for (int j = 1; j <= M; ++j) cango[j] = M;
    for (int i2 = i1; i2 <= N; ++i2) {
      for (int j = 1; j <= M; ++j) {
        if (rg[i2][j] != M + 1) cango[j] = min(cango[j], rg[i2][j] - 1);
        if (lf[i2][j] != 0) cango[lf[i2][j]] = min(cango[lf[i2][j]], j - 1);
      }
      ST[0] = 0;
      for (int j = 1; j <= M; ++j) {
        while (ST[0] != 0 && cango[j] <= cango[ST[ST[0]]]) --ST[0];
        ST[++ST[0]] = j;
      }
      int begnow = 1;
      for (int j = 1; j <= M; ++j) {
        while (j > ST[begnow]) ++begnow;
        result = max(result, (i2 - i1 + 1) * (cango[ST[begnow]] - j + 1));
      }
    }
  }
  cout << result << '\n';
}
