#include <bits/stdc++.h>
#include <unistd.h>
 
using namespace std;
 
#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl
#define DEBUG_MAT(v) cerr<<#v<<endl;for(int i=0;i<v.size();i++){for(int j=0;j<v[i].size();j++) {cerr<<v[i][j]<<" ";}cerr<<endl;}
 
 
typedef long long ll;
#define int ll
 
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rrep1(i,n) for(int i=(n);i>0;i--)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),c.end()
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a = b; return 1; } return 0; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = (ll)1e18 + 1;
const ll MOD = 1000000007;
//const ll MOD = 998244353;
const double pi = 3.14159265358979323846;
#define Sp(p) cout<<setprecision(15)<< fixed<<p<<endl;
int dx[4] = { -1,0, 1,0 }, dy[4] = { 0,1,0,-1 };
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);
// #define mp make_pair
//#define endl '\n'


signed main() {
  fio();
  int h, w;
  cin >> h >> w;
  vector<string> s(h);
  rep (i, h) cin >> s[i];

  vii a(h - 1, vi(w - 1));
  rep (i, h - 1) {
    rep (j, w - 1) {
      int cnt = 0;
      rep (di, 2) rep (dj, 2) {
        if (s[i + di][j + dj] == '#') cnt++;
      }
      if (cnt % 2 == 1) a[i][j] = 1;
    }
  }

  vii nex(h - 1, vi(w - 1));
  rep (j, w - 1) {
    if (a[h - 2][j]) nex[h - 2][j] = h - 2;
    else nex[h - 2][j] = h - 1;

    for (int i = h - 3; i >= 0; i--) {
      nex[i][j] = nex[i + 1][j];
      if (a[i][j]) nex[i][j] = i;
    }
  }

  //DEBUG_MAT(a);
  //DEBUG_MAT(nex);

  int ans = max(h, w);
  rep (i, h - 1) {
    stack<pii> dq;
    rep (j, w - 1) {
      int pre = j;
      while (dq.size() > 0 and dq.top().second > nex[i][j]) {
        pii temp = dq.top();
        dq.pop();
        int hh = temp.second - i;
        int ww = j - temp.first;
        //DEBUG(pii(hh, ww));
        chmax(ans, (hh + 1) * (ww + 1));
        pre = temp.first;
      }
      dq.push(pii(pre, nex[i][j]));
    }
    while (dq.size() > 0) {
      pii temp = dq.top();
      dq.pop();
      int hh = temp.second - i;
      int ww = w - 1 - temp.first;
      //DEBUG(pii(hh, ww));
      chmax(ans, (hh + 1) * (ww + 1));
    }
  }
  cout << ans << endl;
}


Measured memory_bytes: 67072