#include <iostream>
#include <string>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <unordered_map>
#include <map>
#include <set>
#include <algorithm>
#include <queue>
#include <stack>
#include <functional>
#include <bitset>
#include <assert.h>
#include <unordered_map>
#include <fstream>
#include <ctime>
#include <complex>
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<char> vc;
typedef vector<string> vs;
typedef vector<bool> vb;
typedef vector<double> vd;
typedef pair<ll,ll> P;
typedef pair<int,int> pii;
typedef vector<P> vpl;
typedef tuple<ll,ll,ll> tapu;
#define rep(i,n) for(int i=0; i<(n); i++)
#define REP(i,a,b) for(int i=(a); i<(b); i++)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
const int inf = 1<<30;
const ll linf = 1LL<<62;
const int MAX = 510000;
ll dy[8] = {1,-1,0,0,1,-1,1,-1};
ll dx[8] = {0,0,1,-1,1,-1,-1,1};
const double pi = acos(-1);
const double eps = 1e-7;
template<typename T1,typename T2> inline bool chmin(T1 &a,T2 b){
	if(a>b){
		a = b; return true;
	}
	else return false;
}
template<typename T1,typename T2> inline bool chmax(T1 &a,T2 b){
	if(a<b){
		a = b; return true;
	}
	else return false;
}
template<typename T> inline void print(T &a){
    rep(i,a.size()) cout << a[i] << " ";
    cout << "\n";
}
template<typename T1,typename T2> inline void print2(T1 a, T2 b){cout << a << " " << b << "\n";}
template<typename T1,typename T2,typename T3> inline void print3(T1 a, T2 b, T3 c){
	cout << a << " " << b << " " << c << "\n";
}
ll pcount(ll x) {return __builtin_popcountll(x);}
//const int mod = 1e9 + 7;
const int mod = 998244353;

int main(){
	int h,w; cin >> h >> w;
	vs s(h); rep(i,h) cin >> s[i];
	vvl dist(h+1,vl(w,0));
	rep(j,w) rep(k,2) dist[0][j] = w-j;
	int ans = w;
	rep(j,w){
		vector<pii> st;
		st.emplace_back(0,0);
		REP(i,1,h+1){
			if(i < h){
				if(j==0 || dist[i][j-1] == 1){
					int d = 0;
					bool rev = s[i][j] != s[i-1][j];
					REP(k,j,w){
						if(rev == (s[i][k] != s[i-1][k])) d++;
						else break;
					}
					dist[i][j] = d;
				}else{
					dist[i][j] = dist[i][j-1] - 1;
				}
			}
			if(st.empty() || st.back().first < dist[i][j]){
				st.emplace_back(dist[i][j],i);
			}else{
				int pos = i;
				while(!st.empty()){
					if(st.back().first >= dist[i][j]){
						pii p = st.back();
						chmax(ans, p.first*(i-p.second)+p.first);
						pos = p.second;
						st.pop_back();
					}else{
						st.emplace_back(dist[i][j], pos);
						break;
					}
				}
			}
		}
	}
	cout << ans << "\n";
}
//    Have a nice day
//    ∠( ᐛ 」∠)

#include<bits/stdc++.h>

#define mp make_pair
#define pb push_back
#define x first
#define y second

using namespace std;

typedef long long LL;
typedef pair<int,int> pii;

template <typename T> inline T read()
{
	T sum=0, fl=1; char ch=getchar();
	for(; !isdigit(ch); ch=getchar()) if(ch=='-') fl=-1;
	for(; isdigit(ch); ch=getchar()) sum=(sum<<3)+(sum<<1)+ch-'0';
	return sum*fl;
}

const int maxn=2000+5;
int n, m, ans;
char s[maxn][maxn];
int l[maxn], r[maxn], h[maxn], c[maxn][maxn];

void Solve()
{
	n=read<int>(), m=read<int>(); ans=max(n, m);
	for(int i=1; i<=n; ++i) scanf("%s", s[i]+1);
	--n, --m;
	for(int i=1; i<=n; ++i)
		for(int j=1; j<=m; ++j)
			if(((s[i][j]=='#')+(s[i+1][j]=='#')+(s[i][j+1]=='#')+(s[i+1][j+1]=='#'))&1);
			else c[i][j]=1;

	for(int i=1; i<=m; ++i) l[i]=r[i]=maxn;
	for(int i=1; i<=n; ++i)
	{
		for(int j=1, p=0; j<=m; ++j)
		{
			if(c[i][j]) ++p; else p=0;
			l[j]=min(l[j], p);
		}
		for(int j=m, p=0; j>=1; --j)
		{
			if(c[i][j]) ++p; else p=0;
			r[j]=min(r[j], p);
		}
		for(int j=1; j<=m; ++j) 
		{
			if(c[i][j]) ++h[j], ans=max(ans, (l[j]+r[j])*(h[j]+1));
			else l[j]=r[j]=maxn, h[j]=0;
		}
	}
	printf("%d\n", ans);
}

int main()
{

   // freopen("081d.in","r",stdin);
    //freopen("081d.out","w",stdout);

    Solve();

    return 0;
}

