/*
                                                                                                     
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           `o+/::------://o/`           `-` -.          -`       `..`                               
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          `:s+/:--....-::/+s-`      .-   `-                -`           -///:--------:/:`           
           ./s+//:::::://oo-``..НЕЙРОННУЮ: СЕТЬ:::::::-`РАБОТЯГИ        `+:--........--:/`          
            .:ooo+++++osso-`    `.:-...`/` ./::-------:/:`   -`         :+--..``````.--:+:...-+:-`  
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              `.:///////.-`      .:-..` -``-+o+/:::::/+o/.  `-         `:+:-..`````..--:o/:--/ys+-  
            `-++///////+o/. ``....`-.    :` `.:++++++/:.`  .-           -o/---......---/o.   `.`    
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       .` `/s//:--....-::/+s.            -. `-`        .-       `..`                                
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            ./oo++////+oso-`   `....       :y-+:::::::/`   ...                                      
             `.:+oooooo/-`         `....-. .//:-------:/:-.`                                        
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                                         `-o/:---...---:++.                                         
                                          `-+o+/:---:/+o/.                                          
                                            `.:+oooo+/-.`                                           
                                               ``````                                               
*/


#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <map>
#include <set>
#include <queue>
#include <ostream>
#include <istream>
#include <typeinfo>
#include <iomanip>
#include <cstdio>
#include <cstdlib>
#include <cassert>
#include <limits>
#include <fstream>
#include <array>
#include <list>
#include <bitset>
#include <functional>

#define mt make_tuple
#define x first
#define y second
#define pb push_back
#define ppb pop_back
#define pf push_front
#define ppf pop_front
#define mp make_pair
#define umap unordered_map
#define uset unordered_set
#define rt return 0;
#define elif else if
#define len(v) ((int)v.size())


using namespace std;

char string_in_buffer[(int)1e5];


void fast_scan(int &x) { scanf("%d", &x); }
void fast_scan(long long &x) { scanf("%lld", &x); }
void fast_scan(unsigned long long &x) { scanf("%llu", &x); }
void fast_scan(double &x) { scanf("%lf", &x); }
void fast_scan(long double &x) { scanf("%Lf", &x); }
void fast_scan(char &x) { 
	scanf("%c", &x); 
	if (x == '\n') {
		fast_scan(x);
	}
}
void fast_scan(string &x) {
	scanf("%s", string_in_buffer);
	x = string(string_in_buffer);
}

template<class TFirst, class TSecond>
void fast_scan(pair<TFirst, TSecond> &p) {
	fast_scan(p.first);
	fast_scan(p.second);
}

template <class T>
void fast_scan(vector<T> &v) {
	for (auto &x : v) fast_scan(x);
}

void fast_print(const int &x) { printf("%d", x); }
void fast_print(const long long &x) { printf("%lld", x); }
void fast_print(const unsigned long long &x) { printf("%llu", x); }
void fast_print(const double &x) { printf("%.15lf", x); }
void fast_print(const long double &x) { printf("%.15Lf", x); }
void fast_print(const char &x) { printf("%c", x); };
void fast_print(const string &x) { printf("%s", x.c_str());}

template<class TFirst, class TSecond>
void fast_print(const pair<TFirst, TSecond> &p) {
	fast_print(p.first);
	fast_print(' ');
	fast_print(p.second);
}

template <class T>
void fast_print(const vector<T> &v) {
	if (v.empty()) return;
	fast_print(v[0]);
	for (int i = 1; i < v.size(); i++) {
		fast_print(" ");
		fast_print(v[i]);
	}
}

template <class T>
void fast_print(const vector<vector<T>> &v) {
	if (v.empty()) return;
	fast_print(v[0]);
	for (int i = 1; i < v.size(); i++) {
		fast_print("\n");
		fast_print(v[i]);
	}
}



using namespace std;


namespace smart_io {
	string print_start = "";
	string sep = " ";
	bool first_print = false;

	void precall_print() {
		fast_print(print_start);
		print_start = "\n";
		first_print = true;
	}
} //namespace smart_io


template <class T>
ostream &operator,(ostream &os, const T &object) {
	if (!smart_io::first_print) {
		fast_print(smart_io::sep);
	} else {
		smart_io::first_print = false;
	}
	fast_print(object);
	return os;
}

template <class T>
istream &operator,(istream &is, T &object) {
	fast_scan(object);
	return is;
}

#define int long long

namespace typedefs {
	typedef long long ll;
	typedef unsigned long long ull;
	typedef pair<int, int> pii;
	typedef long double ld;
}

namespace numbers_operation {
	template<class T>
	T floor_mod(T a, T b) {
		if (a % b == 0) return 0;
		if (a >= 0 && b >= 0) return a % b;
		if (a <= 0 && b <= 0) return a % b;
		return abs(b) - (abs(a) % abs(b));
	}
}

using namespace numbers_operation;
using namespace typedefs;

#define print    \
smart_io::precall_print(); \
cout,

#define scan cin,

vector<int> _can(32, -1);

int id(const vector<vector<bool>> &v) {
	return v[0][0] + v[0][1] * 2 + v[1][0] * 4 + v[1][1] * 8;
}

vector<vector<vector<bool>>> get_vars(vector<vector<bool>> mt) {
	vector<vector<vector<bool>>> vars;
	vector<vector<bool>> kek(2, vector<bool>(2));
	{
		kek[0][0] = mt[0][0] ^ 1; kek[0][1] = mt[0][1] ^ 1;
		kek[1][0] = mt[1][0]; kek[1][1] = mt[1][1];
		vars.pb(kek);
	}
	{
		kek[0][0] = mt[0][0]; kek[0][1] = mt[0][1];
		kek[1][0] = mt[1][0] ^ 1; kek[1][1] = mt[1][1] ^ 1;
		vars.pb(kek);
	}
	{
		kek[0][0] = mt[0][0] ^ 1; kek[0][1] = mt[0][1];
		kek[1][0] = mt[1][0] ^ 1; kek[1][1] = mt[1][1];
		vars.pb(kek);
	}
	{
		kek[0][0] = mt[0][0]; kek[0][1] = mt[0][1] ^ 1;
		kek[1][0] = mt[1][0]; kek[1][1] = mt[1][1] ^ 1;
		vars.pb(kek);
	}
	return vars;
}

bool normal(vector<vector<bool>> v) {
	int _id = id(v);
	if (v[0][0] + v[0][1] + v[1][0] + v[1][1] == 4) {
		return _can[_id] = true;
	}
	if (_can[_id] == -1) {
		_can[_id] = -2;
		bool kekus = false;
		for (auto sub : get_vars(v)) {
			if (_can[id(sub)] == -2) continue;
			if (_can[id(sub)] == -1) {
				normal(sub);
			}
			if (_can[id(sub)]) {
				kekus = true;
				break;
			}
		}
		_can[_id] = kekus;
	}
	return _can[_id];
}


signed main(signed argc, char *argv[]) {
	for (int mask = 0; mask < 16; mask++) {
		vector<vector<bool>> keks(2, vector<bool>(2));
		keks[0][0] = mask & 1; keks[0][1] = mask & 2;
		keks[1][0] = mask & 4; keks[1][1] = mask & 8;
		if (normal(keks)) {
			// print keks;
			// print "__________________________";
		}
	}
	// return 0;
	int n, m;
	scan n, m;
	vector<vector<bool>> v(n, vector<bool>(m, false));
	for (int i = 0; i < n; i++) {
		string s;
		scan s;
		for (int j = 0; j < m; j++) {
			v[i][j] = (s[j] == '.');
		}
	}
	vector<vector<bool>> norm(n, vector<bool>(m, false));

	for (int i = 1; i < n; i++) {
		for (int j = 1; j < m; j++) {
			norm[i][j] = normal({
				{ v[i - 1][j - 1], v[i - 1][j] },
				{ v[i][j - 1], v[i][j] }
			});
		}
	}

	ll rez = max(n, m);
	vector<vector<int>> up(n, vector<int>(m, 0));
	for (int i = 1; i < n; i++) {
		for (int j = 1; j < m; j++) {
			if (norm[i][j]) {
				up[i][j] = up[i - 1][j] + 1;
			}
		}
	}
	int x = -1;
	int y = -1;
	int w = -1;
	int h = -1;

	for (int i = 0; i < n; i++) {
		vector<int> left(m);
		vector<int> right(m);
		vector<int> st;
		for (int j = 0; j < m; j++) {
			while (!st.empty() && up[i][st.back()] >= up[i][j]) {
				st.pop_back();
			}
			if (st.empty()) {
				left[j] = 0;
			} else {
				left[j] = st.back() + 1;
			}
			st.pb(j);
		}
		st.clear();
		for (int j = m - 1; j > -1; j--) {
			while (!st.empty() && up[i][st.back()] >= up[i][j]) {
				st.pop_back();
			}
			if (st.empty()) {
				right[j] = m - 1;
			} else {
				right[j] = st.back() - 1;
			}
			st.pb(j);
		}
		st.clear();
		for (int j = 0; j < m; j++) {
			if (up[i][j] == 0) continue;
			if (rez < (ll)(right[j] - left[j] + 2) * (ll)(up[i][j] + 1)) {
				rez = (ll)(right[j] - left[j] + 2) * (ll)(up[i][j] + 1);
				// x = i - up[i][j];
				// y = ;
				// w = right[j] - left[j] + 2;
				// h = up[i][j];
			}
		}
	}
	print rez;
}

Measured memory_bytes: 32768