#include<bits/stdc++.h>
using namespace std;
#define pii pair<int,int>
#define X first
#define Y second
const int maxn = 2505;
int n,m;
int p[maxn][maxn];
vector<pii> con[maxn];
set<pii> itv[maxn];
multiset<int> len;
void upd(int x,pii val,int type) {
if(type==0) {
// printf("DEL [%d, %d]\n",val.X,val.Y);
len.erase(len.find(val.Y-val.X+1));
itv[x].erase(val);
}
else {
// printf("ADD [%d, %d]\n",val.X,val.Y);
len.insert(val.Y-val.X+1);
itv[x].insert(val);
}
}
void add(int x,int y) {
int l,r;
set<pii>::iterator L,R;
upd(x,{y,y},1);
l = r = y;
L = R = itv[x].find({y,y});
if(L!=itv[x].begin()) {
--L;
if(L->Y+1==y) {
l = L->X;
upd(x,*L,0);
}
}
++R;
if(R!=itv[x].end()) {
if(R->X-1==y) {
r = R->Y;
upd(x,*R,0);
}
}
upd(x,{y,y},0);
upd(x,{l,r},1);
}
void del(int x,int y) {
int l,r;
set<pii>::iterator it;
it = itv[x].upper_bound({y,m+1});
--it;
l = it->X; r = it->Y;
upd(x,{l,r},0);
if(l<=y-1) upd(x,{l,y-1},1);
if(y+1<=r) upd(x,{y+1,r},1);
}
int main() {
int i,j,x,cnt,bound,ans;
char c;
scanf("%d%d",&n,&m);
for(i=1;i<=n;i++) {
for(j=1;j<=m;j++) {
scanf(" %c",&c);
p[i][j] = c-'0';
}
}
bound = n;
for(j=1;j<=m;j++) {
cnt = 0;
for(i=n;i>=1;i--) {
if(p[i][j]==0) {
if(cnt!=0) bound = min(bound, cnt);
cnt = 0;
}
else cnt++;
con[cnt].push_back({i,j});
}
}
for(i=1;i<=n;i++) for(j=1;j<=m;j++) add(i,j);
ans = 0;
for(x=1;x<=bound;x++) {
// printf("Fixed row = %d\n",x);
for(auto t : con[x-1]) del(t.X,t.Y);
// for(i=1;i<=n;i++) {
// printf("\t");
// for(auto t : itv[i]) printf("[%d, %d] ",t.X,t.Y);
// printf("\n");
// }
if(!len.empty()) ans = max(ans, x*(*len.begin()));
// if(!len.empty()) printf("Minimum = %d\n",*len.begin());
}
printf("%d",ans);
}
