#line 2 "/Users/kaage/Desktop/ProgrammingWorkspace/library/other/template.hpp"
#define _CRT_SECURE_NO_WARNINGS
#pragma target("avx2")
#pragma optimize("O3")
#pragma optimize("unroll-loops")
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <memory>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <string.h>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
#define rep(i,n) for(int i=0;i<(n);i++)
#define REP(i,n) for(int i=1;i<=(n);i++)
#define all(V) V.begin(),V.end()
typedef unsigned int uint;
typedef long long lint;
typedef unsigned long long ulint;
typedef std::pair<int, int> P;
typedef std::pair<lint, lint> LP;
constexpr int INF = INT_MAX/2;
constexpr lint LINF = LLONG_MAX/2;
constexpr double eps = DBL_EPSILON;
constexpr double PI=3.141592653589793238462643383279;
template<class T>
class prique :public std::priority_queue<T, std::vector<T>, std::greater<T>> {};
template <class T, class U>
inline bool chmax(T& lhs, const U& rhs) {
	if (lhs < rhs) {
		lhs = rhs;
		return 1;
	}
	return 0;
}
template <class T, class U>
inline bool chmin(T& lhs, const U& rhs) {
	if (lhs > rhs) {
		lhs = rhs;
		return 1;
	}
	return 0;
}
inline lint gcd(lint a, lint b) {
	while (b) {
		lint c = a;
		a = b; b = c % b;
	}
	return a;
}
inline lint lcm(lint a, lint b) {
	return a / gcd(a, b) * b;
}
bool isprime(lint n) {
	if (n == 1)return false;
	for (int i = 2; i * i <= n; i++) {
		if (n % i == 0)return false;
	}
	return true;
}
template<typename T>
T mypow(T a, lint b) {
	T res(1);
	while(b){
		if(b&1)res*=a;
		a*=a;
		b>>=1;
	}
	return res;
}
lint modpow(lint a, lint b, lint m) {
	lint res(1);
	while(b){
		if(b&1){
			res*=a;res%=m;
		}
		a*=a;a%=m;
		b>>=1;
	}
	return res;
}
template<typename T>
void printArray(std::vector<T>& vec) {
	rep(i, vec.size()){
		std::cout << vec[i];
		std::cout<<(i==(int)vec.size()-1?"\n":" ");
	}
}
template<typename T>
void printArray(T l, T r) {
	T rprev = std::prev(r);
	for (T i = l; i != rprev; i++) {
		std::cout << *i << " ";
	}
	std::cout << *rprev << std::endl;
}
LP extGcd(lint a,lint b) {
	if(b==0)return {1,0};
	LP s=extGcd(b,a%b);
	std::swap(s.first,s.second);
	s.second-=a/b*s.first;
	return s;
}
LP ChineseRem(const lint& b1,const lint& m1,const lint& b2,const lint& m2) {
	lint p=extGcd(m1,m2).first;
	lint tmp=(b2-b1)*p%m2;
	lint r=(b1+m1*tmp+m1*m2)%(m1*m2);
	return std::make_pair(r,m1*m2);
}
template<typename F>
inline constexpr decltype(auto) lambda_fix(F&& f){
	return [f=std::forward<F>(f)](auto&&... args){
		return f(f,std::forward<decltype(args)>(args)...);
	};
}
#line 3 "/Users/kaage/Desktop/ProgrammingWorkspace/library/data-structure/SparseTable.hpp"
template<typename T>
class SparseTable {
	std::vector<std::vector<T>> table;
	std::vector<int> logtable;
public:
	SparseTable(std::vector<T> vec) {
		int maxlength = 0;
		while ((1 << (maxlength + 1)) <= vec.size())maxlength++;
		table.resize(maxlength + 1, std::vector<T>(vec.size()));
		logtable.resize(vec.size() + 1);
		rep(i, maxlength + 1) {
			rep(j, vec.size() - (1 << i) + 1) {
				if (i) {
					table[i][j] = std::min(table[i - 1][j], table[i - 1][j + (1 << (i - 1))]);
				}
				else table[i][j] = vec[j];
			}
		}
		logtable[1] = 0;
		for (int i = 2; i <= vec.size(); i++) {
			logtable[i] = logtable[i >> 1] + 1;
		}
	}
	template<class InputIter>
	SparseTable(InputIter first,InputIter last){
		std::vector<T> vec;
		while(first!=last){
			vec.emplace_back(*first);
		}
	}
	T query(int l, int r) {
		int length = r - l;
		return std::min(table[logtable[length]][l], table[logtable[length]][r - (1 << logtable[length])]);
	}
};
#line 3 "main.cpp"
int H,W;
char s[2010][2010];
std::vector<int> c[2010];
int main(){
	std::cin>>H>>W;
	rep(i,H){
		rep(j,W)std::cin>>s[i][j];
	}
	rep(i,H-1){
		rep(j,W-1){
			if((s[i][j]==s[i][j+1])!=(s[i+1][j]==s[i+1][j+1]))c[i].emplace_back(j);
		}
	}
	int ans=std::max(H,W);
	rep(i,W-1){
		std::vector<P> vec;
		rep(j,H-1){
			auto ite=std::lower_bound(all(c[j]),i);
			int x=ite!=c[j].end()?*ite:W-1;
			vec.emplace_back(x,j);
		}
		std::set<P> interval;
		std::set<int> len;
		interval.insert({0,H});
		len.insert(H);
		std::sort(all(vec));
		int now=0;
		for(int j=i;j<W;j++){
			if((W-i+1)*(*len.rbegin())<=ans)break;
			chmax(ans,(j-i+1)*(*len.rbegin()));
			while(now<vec.size()&&vec[now].first<=j){
				auto ite=--interval.upper_bound({vec[now].second,INF});
				len.erase(ite->second-ite->first);
				interval.insert({ite->first,vec[now].second+1});
				len.insert(vec[now].second+1-ite->first);
				interval.insert({vec[now].second+1,ite->second});
				len.insert(ite->second-vec[now].second-1);
				interval.erase(ite);
				now++;
			}
		}
	}
	std::cout<<ans<<std::endl;
	return 0;
}

Measured memory_bytes: 23316