#define STOPIT
#include <bits/stdc++.h>
#define loop(n) for (lint ngtkana_is_a_genius = 0; ngtkana_is_a_genius < lint(n); ngtkana_is_a_genius++)
#define rep(i, begin, end) for (lint i = lint(begin); (i) < lint(end); i++)
#define all(v) v.begin(), v.end()
#define rand(l, r) std::uniform_int_distribution<>(l, r)(mt)
using lint = long long;
auto mt = std::mt19937_64(std::random_device{}());
auto cmn = [](auto& a, auto b){ if (a > b) {a = b; return true;} return false; };
auto cmx = [](auto& a, auto b){ if (a < b) {a = b; return true;} return false; };
void debug_impl() { std::cerr << std::endl; }
template <typename Head, typename... Tail>
void debug_impl(Head head, Tail... tail) { std::cerr << " " << head; debug_impl(tail...); }
#ifndef STOPIT
#define debug(...)\
	do {\
		std::cerr << std::boolalpha << "[" << #__VA_ARGS__ << "]:";\
		debug_impl(__VA_ARGS__);\
		std::cerr << std::noboolalpha;\
	} while (false)
#else
#define debug(...) {}
#endif

template <typename T>
auto make_vector_impl(size_t sz, T t) {return std::vector<T>(sz, t);}

template <size_t N, typename T, typename U, std::enable_if_t<N == 1, std::nullptr_t> = nullptr>
auto make_vector(size_t sz, U u) {return make_vector_impl(sz, T(u));}

template <size_t N, typename T, std::enable_if_t<N == 1, std::nullptr_t> = nullptr>
auto make_vector(size_t sz) {return std::vector<T>(sz);}

template <size_t N, typename T, typename... Args, std::enable_if_t<N != 1, std::nullptr_t> = nullptr>
auto make_vector(size_t a, Args... args) {return make_vector_impl(a, make_vector<N - 1, T>(args...));}

template <typename T, typename Size_t>
auto& at(T& t, Size_t i) {return t.at(i);}

template <typename T, typename Size_t, typename... Args>
auto& at(T& t, Size_t i, Args... args) {return at(t.at(i), args...);}

template < typename Container, typename Value = typename Container::value_type, std::enable_if_t<!std::is_same< Container, std::string >::value, std::nullptr_t> = nullptr>
std::istream& operator>> (std::istream& is, Container& v)
	{ for (auto & x : v) { is >> x; } return is; }

template < typename Container, typename Value = typename Container::value_type, std::enable_if_t<!std::is_same< Container, std::string >::value, std::nullptr_t> = nullptr >
std::ostream& operator<< (std::ostream& os, Container const& v) {
 os << "{";
	for (auto it = v.begin(); it != v.end(); it++)
		{os << (it != v.begin() ? "," : "") << *it;}
	return os << "}";
}

int main() {
	std::cin.tie(0); std::cin.sync_with_stdio(false);
	int h, w; std::cin >> h >> w;
	auto a = make_vector<2,int>(h,w);
	rep(i,0,h) rep(j,0,w) {
		char c; std::cin >> c;
		at(a,i,j) = c == '#';
	}

	auto b = make_vector<2,int>(h+1,w+1,1);
	rep(i,1,h) rep(j,1,w) {
		int x = 0;
		rep(di,0,2) rep(dj,0,2) {
			x += at(a,i-di,j-dj);
		}
		at(b,i,j) = x % 2;
	}

	auto c = make_vector<2,int>(h+1,w+1,0);
	rep(i,0,h) rep(j,1,w) {
		int x = at(c,i,j);
		if (at(b,i,j)) x = 0;
		x++;
		at(c,i+1,j) = x;
	}

	// debug
	// for (auto& v : a) debug(v);
	// debug("");
	// for (auto& v : b) debug(v);
	// debug("");
	// for (auto& v : c) debug(v);
	// debug("");

	int ans = std::max(h,w);
	for (auto& v : c) {
		debug(v);
		std::stack<std::pair<int,int>> stack;
		assert((int)v.size() == w + 1);
		rep(i,0,w+1) {
			int x = v.at(i);
			while (!stack.empty() && x < stack.top().second) {
				int j,y; std::tie(j,y) = stack.top(); stack.pop();
				debug(i,j,i-j+1,y);
				int now = (i-j+1)*y;
				cmx(ans, now);
				if (!stack.empty() && stack.top().second < x) {
					stack.emplace(j,x);
				}
			}
			if (stack.empty() || stack.top().second < x) {
				stack.emplace(i,x);
			}
		}
	}
	std::cout << ans << std::endl;
	return 0;
}

Measured memory_bytes: 47360