#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<set>
#include<bitset>
#include<map>

#define fo(i,a,b) for(int i=a;i<=b;i++)
#define fd(i,a,b) for(int i=a;i>=b;i--)

using namespace std;

typedef long long LL;
typedef double db;

int get(){
	char ch;
	while(ch=getchar(),(ch<'0'||ch>'9')&&ch!='-');
	if (ch=='-'){
		int s=0;
		while(ch=getchar(),ch>='0'&&ch<='9')s=s*10+ch-'0';
		return -s;
	}
	int s=ch-'0';
	while(ch=getchar(),ch>='0'&&ch<='9')s=s*10+ch-'0';
	return s;
}

const int N = 2005;

int H,W;
char mp[N][N];
int a[N][N];
int h[N];
int sta[N],top;

int main(){
	H=get();W=get();
	fo(i,1,H)scanf("%s",mp[i]+1);
	fo(i,1,H)
		fo(j,2,W)a[i][j]=(mp[i][j]==mp[i][j-1]);
	int ans=0;
	fo(i,1,H){
		fo(j,1,W)
		if (a[i][j]==a[i-1][j])h[j]++;else h[j]=1;
		sta[0]=1;
		sta[top=1]=1;
		fo(j,2,W){
			while(top&&h[sta[top]]>=h[j]){
				ans=max(ans,h[sta[top]]*(j-sta[top-1]));
				top--;
			}
			sta[++top]=j;
		}
		fo(j,1,top)ans=max(ans,h[sta[j]]*(W-sta[j-1]+1));
	}
	printf("%d\n",ans);
	return 0;
}