#include <bits/stdc++.h>
using namespace std;
template <typename T1, typename T2>
inline T1 max(T1 a, T2 b) {
  return a < b ? b : a;
}
template <typename T1, typename T2>
inline T1 min(T1 a, T2 b) {
  return a < b ? a : b;
}
namespace ae86 {
const int bufl = 1 << 15;
char buf[bufl], *s = buf, *t = buf;
inline int fetch() {
  if (s == t) {
    t = (s = buf) + fread(buf, 1, bufl, stdin);
    if (s == t) return EOF;
  }
  return *s++;
}
inline int ty() {
  int a = 0, b = 1, c = fetch();
  while (!isdigit(c)) b ^= c == '-', c = fetch();
  while (isdigit(c)) a = a * 10 + c - 48, c = fetch();
  return b ? a : -a;
}
}  // namespace ae86
using ae86::ty;
const int _ = 407, __ = 160007;
int n, m, val[_][_], ans[_][_], ed[__] = {0}, xl[_], xr[_];
int main() {
  n = ty(), m = ty();
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++) val[i][j] = ty();
  memset(ans, 63, sizeof(ans));
  int sans = 0;
  for (int d = 1; d <= n; d++) {
    for (int i = 1; i <= m; i++) xl[i] = 0, xr[i] = m + 1;
    for (int u = d; u >= 1; u--) {
      for (int i = 1, j = 1; i <= m; i++) {
        j = max(j, i);
        while (j < xr[i] && !ed[val[u][j]] && !ed[val[d][j]]) {
          if (val[u][j] == val[d][j] && u != d) break;
          ed[val[u][j]] = ed[val[d][j]] = 1, j++;
        }
        ed[val[u][i]] = ed[val[d][i]] = 0, xr[i] = min(xr[i], j);
      }
      for (int i = m, j = m; i >= 1; i--) {
        j = min(j, i);
        while (j > xl[i] && !ed[val[u][j]] && !ed[val[d][j]]) {
          if (val[u][j] == val[d][j] && u != d) break;
          ed[val[u][j]] = ed[val[d][j]] = 1, j--;
        }
        ed[val[u][i]] = ed[val[d][i]] = 0, xl[i] = max(xl[i], j);
      }
      for (int i = 1; i <= m; i++)
        ans[u][i] = min(ans[u][i], xr[i] - 1),
        ans[u][xl[i]] = min(ans[u][xl[i]], i - 1);
      for (int i = m; i >= 1; i--)
        ans[u][i] = min(ans[u][i], ans[u][i + 1]),
        sans = max(sans, (d - u + 1) * (ans[u][i] - i + 1));
    }
  }
  printf("%d\n", sans);
  return 0;
}
