#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N = 2542, INF = 1e18 + 42;
vector<pair<int, int>> pos[N];
int n, m, val[N][N], occ[N], sz[N][N];
int F(int lig, int col) {
if(sz[lig][col] < 0)
return lig * m + col;
return sz[lig][col] = F(sz[lig][col] / m, sz[lig][col] % m);
}
void U(int l1, int c1, int l2, int c2) {
int a = F(l1, c1), b = F(l2, c2);
if(a == b) return;
occ[-sz[a / m][a % m]]--;
occ[-sz[b / m][b % m]]--;
sz[a / m][a % m] += sz[b / m][b % m];
sz[b / m][b % m] = a;
occ[-sz[a / m][a % m]]++;
}
signed main() {
ios::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
cin >> n >> m;
for(int i = 0; i < n; i++)
for(int j = 0; j < m; j++) {
char c; cin >> c;
val[i][j] = (int)(c - '0');
sz[i][j] = -INF;
}
for(int i = 0; i < n; i++)
for(int j = 1; j < m; j++)
if(val[i][j] == 1)
val[i][j] += val[i][j-1];
int bound = INF;
for(int i = 0; i < n; i++)
for(int j = 0; j < m; j++) {
if(val[i][j] > 0 && val[i][j+1] == 0)
bound = min(bound, val[i][j]);
pos[val[i][j]].push_back({i, j});
}
if(bound == INF) {
cout << "0\n";
return 0;
}
int ans = 0;
for(int i = N-1; i > 0; i--) {
for(auto pii : pos[i]) {
occ[1]++;
int lig = pii.first,
col = pii.second;
sz[lig][col] = -1;
if(0 < lig && val[lig-1][col] >= i && sz[lig-1][col] != -INF)
U(lig, col, lig-1, col);
if(lig < n-1 && val[lig+1][col] >= i && sz[lig+1][col] != -INF)
U(lig, col, lig+1, col);
}
if(i <= bound) {
int mini = 0;
for(int j = N-1; j > 0; j--)
if(occ[j])
mini = j;
ans = max(ans, mini * i);
}
}
cout << ans << '\n';
}
