#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#pragma GCC optimize("unroll-loops")
//#pragma warning(disable : 4996)

#ifdef _MSC_VER
#include <intrin.h>
#define __builtin_popcount __popcnt
#define __builtin_popcountll __popcnt64
#endif

#include <limits.h>
#include <math.h>
#include <time.h>

#include <algorithm>
#include <array>
#include <bitset>
#include <cassert>
#include <complex>
#include <cstdio>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>

using namespace std;

#define REP(i, n) for (int i = 0; i < (n); ++i)
#define REPR(i, n) for (int i = n - 1; i >= 0; --i)
#define FOR(i, m, n) for (int i = m; i < n; ++i)
#define FORR(i, m, n) for (int i = m - 1; i >= n; --i)
#define SORT(v, n) sort(v, v + n);
#define VSORT(v) sort(v.begin(), v.end());
#define REVERSE(v, n) reverse(v, v + n);
#define VREVERSE(v) reverse(v.begin(), v.end())
#define ll long long
#define print(x) cout << (x) << '\n'
#define pe(x) cout << (x) << " "
#define DEBUG(x) cout << #x << ": " << x << endl
#define lb(v, n) lower_bound(v.begin(), v.end(), (n))
#define ub(v, n) upper_bound(v.begin(), v.end(), (n))
#define int long long
#define double long double
#define all(x) (x).begin(), (x).end()
#define print_space(v) REP(i, v.size()) cout << v[i] << ((i == v.size() - 1) ? "\n" : " ")
template <typename T1, typename T2> inline void chmin(T1& a, T2 b) {
	if (a > b) a = b;
}
template <typename T1, typename T2> inline void chmax(T1& a, T2 b) {
	if (a < b) a = b;
}
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
typedef array<int, 3> arr3;
std::random_device rd;
std::mt19937 mt(rd());
constexpr ll MOD = 998244353;
constexpr int MAX = 500050;
const double pi = acos(-1);
constexpr double EPS = 1e-8;
constexpr ll LINF = 1e18 + 1;
constexpr int INF = 1e18 + 1;



int slv(vector<vector<bool>>&C, int H, int W) {
	vector<vector<int>>cnt(H, vector<int>(W-1));
	REP(j, W-1) {
		REP(i, H) {
			if (i == 0)cnt[i][j] = 1;
			else {
				if (C[i][j] == C[i - 1][j])cnt[i][j] = cnt[i - 1][j] + 1;
				else cnt[i][j] = 1;
			}
			//if (C[i][j] == 0)cnt[i][j] = 0;
			//else {
			//	if (i == 0)cnt[i][j] = 1;
			//	else cnt[i][j] = cnt[i - 1][j] + 1;
			//}
		}
	}
	//REP(i, H) {
	//	REP(j, W - 1) {
	//		cout << cnt[i][j] << " ";
	//	}cout << endl;
	//}
	ll ret = H;
	REP(i, H) {
		stack<pii>stk;
		REP(j, W - 1) {
			if (stk.empty()) {
				stk.push({ cnt[i][j],j });
			}
			else {
				pii p = stk.top();
				if (p.first < cnt[i][j])stk.push({ cnt[i][j],j });
				else if (p.first > cnt[i][j]) {
					int r = j+1;
					int h = p.first;
					int pos = j;
					while (!stk.empty()&&h >= cnt[i][j]) {
						pii now = stk.top();
						h = now.first;
						if (h < cnt[i][j])break;
						pos = now.second;
						chmax(ret, h*(r - pos));
						stk.pop();
					}
					stk.push({ cnt[i][j],pos });
				}
			}
		}
		int r = W;
		while (!stk.empty()) {
			pii now = stk.top();
			int h = now.first, pos = now.second;
			chmax(ret, h*(r - pos));
			stk.pop();
		}
	}
	return ret;
}

int calc(vector<vector<char>>&A,int H,int W) {
	vector<vector<bool>>B(H, vector<bool>(W)),C(H,vector<bool>(W-1));
	REP(i, H) {
		REP(j, W) {
			B[i][j] = (A[i][j] == '#') ? 1 : 0;
		}
	}
	//cout << endl;
	REP(i, H) {
		REP(j, W - 1) {
			C[i][j] = B[i][j] ^ B[i][j + 1];
			//cout << C[i][j];
		}//cout << endl;
	}
	ll ret = 0;
	//print(slv(C, H, W));
	ret = max(ret, slv(C, H, W));
	REP(i, H)REP(j, W - 1) {
		C[i][j] = !C[i][j];
	}
	//cout << endl;
	//REP(i, H) {
	//	REP(j, W - 1) {
	//		cout << C[i][j];
	//	}cout << endl;
	//}
	//print(slv(C, H, W));
	ret = max(ret, slv(C, H, W));
	return ret;

}

void solve() {
	int H, W; cin >> H >> W;
	vector<vector<char>>A(H, vector<char>(W)), A2(W, vector<char>(H));
	REP(i, H) {
		REP(j, W) {
			cin >> A[i][j];
			A2[j][i] = A[i][j];
		}
	}
	int ans = 0;
	chmax(ans,calc(A, H, W));
	chmax(ans, calc(A2, W, H));
	print(ans);
}



signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	//mt.seed((int)(time(0)));
	//REP(_, 10000)test();
	//int q;
	//cin >> q;
	//while (q--)
	solve();
}



Measured memory_bytes: 42752