#include <bits/stdc++.h>
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2")
#define int long long
#define pii pair<int,int>
#define vi vector<int>
#define ff first
#define ss second
#define sp << " " <<
#define all(x) x.begin(),x.end()
#define big(x) ((int)(x.size()))
using namespace std;
const int MOD = 1e9+7, LIM = 1e6+1, inf = 2e9;
const int N = 1e5+1;
struct DSU {
multiset<int> strips;
vi dad,sz;
DSU(int m) {
dad.resize(m);
sz.assign(m,0);
iota(all(dad),0ll);
}
int find(int x) {
if (x == dad[x]) return x;
return dad[x] = find(dad[x]);
}
int getstrip(int x) {
return sz[find(x)];
}
void activate(int x) {
sz[x] = 1;
strips.insert(1);
}
void merge(int x,int y) {
int a = find(x),b = find(y);
assert(a != b);
strips.erase(strips.find(getstrip(a)));
strips.erase(strips.find(getstrip(b)));
dad[a] = b;
sz[b]+=sz[a];
strips.insert(getstrip(a));
}
};
void solve() {
int n,m;
cin >> n >> m;
vector<string> grid(n);
for (auto& row : grid) cin >> row;
vector<DSU> dsu(n,DSU(m));
int h[n][m];
vector<pii> ppl[n+1];
for (int i = 0;i<n;i++) {
for (int j = 0;j<m;j++) {
if (grid[i][j] == '0') {
h[i][j] = 0;
continue;
}
if (!i) h[i][j] =1;
else h[i][j] = h[i-1][j]+1;
ppl[h[i][j]].push_back({i,j});
}
}
vector<vi> active(n,vi(m,0));
set<pii> st;
for (int i = 0;i<n;i++) st.insert({inf,i});
vi anss(n,inf);
auto activate = [&](int r,int c) -> void {
active[r][c] = 1;
dsu[r].activate(c);
st.erase({anss[r],r});
if (c && active[r][c-1]) dsu[r].merge(c-1,c);
if (c<m-1 && active[r][c+1]) dsu[r].merge(c,c+1);
anss[r] = *dsu[r].strips.begin();
st.insert({anss[r],r});
};
int ans = 0;
for (int i = n;i>=1;i--) {
for (auto it : ppl[i]) {
activate(it.ff,it.ss);
}
if (st.begin()->first != inf) ans = max(ans,i*st.begin()->first);
}
cout << ans << '\n';
}
signed main() {
ios_base::sync_with_stdio(0); cin.tie(0);
#ifdef Dodi
freopen("in.txt", "r", stdin);
freopen("out.txt", "w", stdout);
#endif
int t = 1;
//cin >> t;
while (t --> 0) solve();
}
