#include <iostream>
#include <string>
#include <cmath>
#include<algorithm>
#include<stack>
#include<queue>
#include<map>
#include<set>
#include<iomanip>
#define _USE_MATH_DEFINES
#include <math.h>
#include <functional>
#include<complex>
using namespace std;

#define rep(i,x) for(ll i=0;i<x;i++)
#define repn(i,x) for(ll i=1;i<=x;i++)

typedef long long ll;
const ll INF = 1e17;
const ll MOD = 1000000007;
const ll MAX = 4000001;
const double eps = 1E-18;

ll max(ll a, ll b) {
	if (a > b) { return a; }
	return b;
}

ll min(ll a, ll b) {
	if (a > b) { return b; }
	return a;
}

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

ll lcm(ll a, ll b) {
	return a / gcd(a, b) * b;
}

struct edge {
	ll ind;
	ll fr;
	ll to;
	ll d;
};

class mint {
	long long x;
public:
	mint(long long x = 0) : x((x% MOD + MOD) % MOD) {}
	mint operator-() const {
		return mint(-x);
	}
	mint& operator+=(const mint& a) {
		if ((x += a.x) >= MOD) x -= MOD;
		return *this;
	}
	mint& operator-=(const mint& a) {
		if ((x += MOD - a.x) >= MOD) x -= MOD;
		return *this;
	}
	mint& operator*=(const  mint& a) {
		(x *= a.x) %= MOD;
		return *this;
	}
	mint operator+(const mint& a) const {
		mint res(*this);
		return res += a;
	}
	mint operator-(const mint& a) const {
		mint res(*this);
		return res -= a;
	}
	mint operator*(const mint& a) const {
		mint res(*this);
		return res *= a;
	}

	mint operator^(const ll& t)const {
		if (!t) return 1;
		mint a = pow(t >> 1);
		a *= a;
		if (t & 1) a *= *this;
		return a;
	}

	mint pow(ll t) const {
		if (!t) return 1;
		mint a = pow(t >> 1);
		a *= a;
		if (t & 1) a *= *this;
		return a;
	}
	// for prime MOD
	mint inv() const {
		return pow(MOD - 2);
	}
	mint& operator/=(const mint& a) {
		return (*this) *= a.inv();
	}
	mint operator/(const mint& a) const {
		mint res(*this);
		return res /= a;
	}

	friend ostream& operator<<(ostream& os, const mint& m) {
		os << m.x;
		return os;
	}
};

///////////////////////////


int main() {
	ll H, W;
	cin >> H >> W;

	vector<vector<char>> s(H, vector<char>(W));
	rep(i, H)rep(j, W) cin >> s[i][j];

	vector<vector<bool>> a(H, vector<bool>(W,0));
	repn(i, H - 1)repn(j, W - 1) {
		ll c = 0;
		if (s[i][j] == '#') { c++; }
		if (s[i][j-1] == '#') { c++; }
		if (s[i-1][j] == '#') { c++; }
		if (s[i-1][j-1] == '#') { c++; }

		if (c % 2 == 0) { a[i][j] = 1; }
	}

	vector<vector<ll>> up(H, vector<ll>(W, 0));
	repn(i, H - 1)repn(j, W - 1) {
		if (a[i][j] == 1) { up[i][j] = up[i-1][j] + 1; }
		else { up[i][j] = 0; }
	}

	

	ll ans = 0;

	repn(i, H-1) {
		vector<ll> L(W), R(W);

		stack<ll> st;

		repn(j, W - 1) {
			while (!st.empty() && up[i][j] <= up[i][st.top()]) { st.pop(); }

			if (st.empty()) { L[j] = 1; }
			else { L[j] = st.top() + 1; }

			
			st.push(j);
		}
		
		while (!st.empty()) { st.pop(); }

		for (ll j = W - 1; j >= 1; j--) {
			while (!st.empty() && up[i][j] <= up[i][st.top()]) { st.pop(); }
			if (st.empty()) { R[j] = W - 1; }
			else { R[j] = st.top() - 1; }

			st.push(j);
		}
		
		repn(j, W - 1) {
			ans = max(ans, (R[j] - L[j] + 2)*(up[i][j] + 1));
		}

	}

	ans = max(ans, H);

	cout << ans << endl;
	
	system("PAUSE");
}


Measured memory_bytes: 38272