#include<cstdio>
#include<cstring>
#include<algorithm>
#define N 1001
using namespace std;
int n,m,k,minn,ans;
char s[N+2][N+2],t[N+2][N+2];
int l[N],r[N];
int a[N],b[N];
int q[N],tmp[N],head,tail;
void change(char w,char x,char y,char z)
{
    for(int i=1;i<=n;i++)
     for(int j=1;j<=m;j++)
      if(s[i][j]==x || s[i][j]==y || s[i][j]==z) t[i][j]=w;
      else t[i][j]=s[i][j]; 
}
void monotonous(int *c,int *d)
{
    int h=1;
    while(h<=m && !c[h]) h++;
    if(h>m) return;
    q[0]=c[h]; tmp[0]=h;
    head=0; tail=1;
    for(int i=h+1;i<=m;i++)
    {
        if(!c[i]) while(head<tail) d[tmp[head++]]=i-1;
        else if(head==tail) q[tail]=c[i],tmp[tail++]=i;
        else
        {
            while(head<tail && c[i]<q[tail-1]) d[tmp[--tail]]=i-1;
            q[tail]=c[i];
            tmp[tail++]=i;
        }
    }
    while(head<tail) d[tmp[head++]]=tmp[tail-1];
}
void solve(char x)
{
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=m;j++)
        {
            if(t[i][j]!=x) a[j]=b[m-j+1]=0;
            else
            {
                if(t[i][j]==t[i-1][j]) a[j]++,b[m-j+1]++;
                 else a[j]=b[m-j+1]=1;
            }
        }
        monotonous(a,r);
        monotonous(b,l);
        for(int j=1;j<=m;j++) tmp[j]=l[j];
        for(int j=1;j<=m;j++) l[m-j+1]=m-tmp[j]+1;
        for(int j=1;j<=m;j++) ans=max(ans,(r[j]-l[j]+1)*a[j]);
    }
}
int main()
{
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        ans=0;
        for(int i=1;i<=n;i++) scanf("%s",s[i]+1);
        change(‘a‘,‘w‘,‘y‘,‘z‘); solve(‘a‘);
        change(‘b‘,‘w‘,‘x‘,‘z‘); solve(‘b‘);
        change(‘c‘,‘x‘,‘y‘,‘z‘); solve(‘c‘);
        printf("%d\n",ans);
    }
}