#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <iostream>
#include <istream>
#include <iterator>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
//#include <tuple>
#include <iomanip>
#include <cstring>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef vector<ll> vec;
typedef vector<vec> mat;
#define rep(i, n) for(ll i = 0; i < (n); i++)
#define revrep(i, n) for(ll i = (n-1); i >= 0; i--)
#define pb push_back
#define f first
#define s second
ll max(ll a, ll b){return (a > b) ? a : b;}
ll min(ll a, ll b){return (a < b) ? a : b;}
ll max3(ll a, ll b, ll c){return max(a, max(b, c));};
ll min3(ll a, ll b, ll c){return min(a, min(b, c));};
ll max4(ll a, ll b, ll c, ll d){return max(max(a, b), min(c, d));};
ll min4(ll a, ll b, ll c, ll d){return min(min(a, b), min(c, d));};
ll max5(ll a, ll b, ll c, ll d, ll e){return max(max(a, b), max3(c, d, e));};
ll min5(ll a, ll b, ll c, ll d, ll e){return min(min(a, b), min3(c, d, e));};

const ll INFL = 1LL << 60;//10^18 = 2^60
const int INF = 1 << 30;//10^9
ll MOD = 1000000007;
//ll MOD = 998244353;
/*
vector<ll> dy = {0, 0, 1, -1, 1, 1, -1, -1, 0};
vector<ll> dx = {1, -1, 0, 0, 1, -1, 1, -1, 0};
*/

ll pow_long(ll x, ll k){
  ll res = 1;
  while(k > 0){
    if(k % 2) res *= x;
    x *= x;
    k /= 2;
  }
  return res;
}
ll pow_mod(ll x, ll k){
  x %= MOD; x += MOD; x %= MOD;
  ll res = 1;
  while(k > 0){
    if(k % 2){
      res *= x; res %= MOD;
    }
    x *= x; x %= MOD;
    k /= 2;
  }
  return res;
}

ll inverse(ll x){return pow_mod(x, MOD - 2);};

ll gcd(ll a, ll b){
    if(b == 0) return a;
    return gcd(b, a % b);
}

ll lcm(ll x, ll y){return x / gcd(x, y) * y;};

ll kai_mod(ll x){
  if(x == 0) return 1;
  return x * kai_mod(x-1) % MOD;
}

/*
//コンビネーション
const int MAXcomb = 200010;
ll fac[MAXcomb], finv[MAXcomb], inv[MAXcomb];
//facはn!,finvは1/n!
//invは逆元
void COMinit(){
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for(int i = 2; i < MAXcomb; i++){
        fac[i] = fac[i-1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD/i) % MOD;
        finv[i] = finv[i-1] * inv[i] % MOD;
    }
}
ll comb(int n, int k){
    if(n < k) return 0;
    if(n < 0 || k < 0) return 0;
    return fac[n] * finv[k] % MOD * finv[n-k] % MOD;
}
*/

ll max_rect(vector<ll> h){
  ll N = h.size();
  ll L[N], R[N];
  //L[i], j <= i かつh_(j-1) < h_iとなる最大のj
  //R[i], i < j かつh_j > h_iとなる最小のj
  //[L, R)
  stack<ll> sta;
  rep(i, N){
    while(!sta.empty() && h[sta.top()] >= h[i]) sta.pop();
    if(sta.empty()) L[i] = 0;
    else{
      L[i] = sta.top() + 1;//[)にするため
    }
    sta.push(i);
  }

  while(!sta.empty()) sta.pop();
  revrep(i, N){
    while(!sta.empty() && h[sta.top()] >= h[i]) sta.pop();
    if(sta.empty()) R[i] = N;
    else{
      R[i] = sta.top();
    }
    sta.push(i);
  }

  ll res = 0;
  rep(i, N){
    if(h[i] == 0 || R[i] == L[i]) continue;
    res = max(res, (h[i] + 1) * (R[i] - L[i] + 1));
  }
  return res;
}

ll H, W;
char mp[2010][2010];
bool ok[2010][2010];
ll R[2010][2010];//一番近いダメなとこ
int main(){
  cin >> H >> W;
  rep(i, H)rep(j, W) cin >> mp[i][j];
  rep(i, H-1)rep(j, W-1){
    ll cnt = 0;
    if(mp[i][j] == '#') cnt++;
    if(mp[i][j+1] == '#') cnt++;
    if(mp[i+1][j] == '#') cnt++;
    if(mp[i+1][j+1] == '#') cnt++;
    if(cnt % 2 == 0) ok[i][j] = 1;
  }

  rep(i, H-1){
    rep(k, W){
      if(ok[i][k]) continue;
      else{
        R[i][0] = k;
        break;
      }
    }
  }

  rep(i, H-1){
    for(ll j = 1; j < W-1; j++){
      if(j < R[i][j-1]) R[i][j] = R[i][j-1];
      else{
        for(ll k = j; k < W; k++){
          if(ok[i][k]) continue;
          else{
            R[i][j] = k;
            break;
          }
        }
      }
    }
  }

  ll ans = max(H, W);
  rep(j, W-1){
    vector<ll> histo(H-1, 0);
    rep(i, H-1){
      histo[i] = R[i][j] - j;
    }
    ans = max(ans, max_rect(histo));
  }
  cout << ans << endl;
}


Measured memory_bytes: 39808