#include <cstdio>
#include <vector>
using namespace std;
int n,m,i,H[220],M[220][220],val=0,j,extst[220],extdr[220],k,k2,Max,posi,posj,h,lst,ldr,Max2,limit,sol=0;
char c;
bool ok;
vector <int> v;

int inline dreptunghi(int val,int n,int m,int n1,int m1)
{
    int Max=0,i,j;
    for(j=m1; j<=m; ++j)
        H[j]=0;
    for(i=n1; i<=n; ++i)
    {
        for(j=m1; j<=m; ++j)
        {
            if(M[i][j]!=val)
                H[j]=0;
            else
            {
                if(H[j]>0)
                    ++H[j];
                else H[j]=1;
            }
        }
        v.clear();
        k=m1;
        while(k<=m)
        {
            if(H[k]==0)
                extst[k]=0,++k;
            else
            {
                limit=k;
                while(H[k]!=0 && k<=m)
                {
                    ok=false;
                    v.push_back(k);
                    extst[k]=1;
                    while(v[v.size()-2]>=limit && v.size()>1 && H[v[v.size()-2]]>=H[v[v.size()-1]] && k<=m)
                    {
                        ok=true;
                        extst[k]+=extst[v[v.size()-2]];
                        v.pop_back();
                        v.pop_back();
                        v.push_back(k);
                        ++k;
                    }
                    if(!ok)
                        ++k;

                }
            }

        }
        v.clear();
        k=m;
        while(k>=m1)
        {
            if(H[k]==0)
                extdr[k]=0,--k;
            else
            {
                limit=k;
                while(H[k]!=0 && k>=m1)
                {
                    ok=false;
                    v.push_back(k);
                    extdr[k]=1;
                    while(k>=m1 &&v[v.size()-2]<=limit && v.size()>1 && H[v[v.size()-2]]<=H[v[v.size()-1]])
                    {
                        extdr[k]+=extdr[v[v.size()-2]];
                        ok=true;
                        v.pop_back();
                        v.pop_back();
                        v.push_back(k);
                        --k;
                    }
                    if(!ok)
                        --k;

                }

            }

        }
        for(j=1; j<=m; ++j)
            if((extst[j]+extdr[j]-1)*H[j]>Max)
            {
                Max=(extst[j]+extdr[j]-1)*H[j];
                posi=i;
                posj=j;
                h=H[j];
                lst=extst[j]-1;
                ldr=extdr[j]-1;
            }
    }
    return Max;
}
int main()
{
    freopen("bmatrix.in","r",stdin);
    freopen("bmatrix.out","w",stdout);
    scanf("%d %d\n",&n,&m);
    for(i=1; i<=n; ++i)
    {
        for(j=1; j<=m; ++j)
        {
            scanf("%c ",&c);
            M[i][j]=c-'0';
        }
        scanf("\n");
    }
    for(i=1; i<n; ++i)
    {
        val=dreptunghi(0,i,m,1,1);
        val+=dreptunghi(0,n,m,i+1,1);
        if(sol<val)
            sol=val;
    }

    val=dreptunghi(0,n,m,1,1);
    if(val>sol)
        sol=val;
    for(j=1; j<m; ++j)
    {
        val=dreptunghi(0,n,j,1,1);
        val+=dreptunghi(0,n,m,1,j+1);
        if(sol<val)
            sol=val;
    }
    printf("%d\n",sol);
    return 0;
}