#include <stdio.h>
#define N 2500
#define M 2500
int min(int a, int b) { return a < b ? a : b; }
int max(int a, int b) { return a > b ? a : b; }
int main() {
static char cc[N][M + 1];
static int ll[N][M], rr[N][M], uu[N][M], dd[N][M], yy[N + 1];
int n, m, i, i_, j, j_, l, r, u, d, x, y, ans;
scanf("%d%d", &n, &m);
for (i = 0; i < n; i++)
scanf("%s", cc[i]);
for (i = 0; i < n; i++) {
for (j = 0; j < m; j++)
ll[i][j] = cc[i][j] == '0' ? j + 1 : (j == 0 ? 0 : ll[i][j - 1]);
for (j = m - 1; j >= 0; j--)
rr[i][j] = cc[i][j] == '0' ? j - 1 : (j + 1 == m ? m - 1 : rr[i][j + 1]);
}
for (j = 0; j < m; j++) {
for (i = 0; i < n; i++)
uu[i][j] = cc[i][j] == '0' ? i + 1 : (i == 0 ? 0 : uu[i - 1][j]);
for (i = n - 1; i >= 0; i--)
dd[i][j] = cc[i][j] == '0' ? i - 1 : (i + 1 == n ? n - 1 : dd[i + 1][j]);
}
for (x = 1; x <= n; x++)
yy[x] = m;
for (i = 0; i < n; i++)
for (j = 0; j < m; j++) {
if (ll[i][j] == j) {
j_ = j, u = 0, d = n - 1;
while (j_ <= rr[i][j]) {
u = max(u, uu[i][j_]), d = min(d, dd[i][j_]);
x = d - u + 1, y = j_ - j;
if (x < n)
yy[x + 1] = min(yy[x + 1], y);
j_++;
}
x = 0, y = j_ - j;
if (x < n)
yy[x + 1] = min(yy[x + 1], y);
}
if (rr[i][j] == j) {
j_ = j, u = 0, d = n - 1;
while (j_ >= ll[i][j]) {
u = max(u, uu[i][j_]), d = min(d, dd[i][j_]);
x = d - u + 1, y = j - j_;
if (x < n)
yy[x + 1] = min(yy[x + 1], y);
j_--;
}
x = 0, y = j - j_;
if (x < n)
yy[x + 1] = min(yy[x + 1], y);
}
if (uu[i][j] == i) {
i_ = i, l = 0, r = m - 1;
while (i_ <= dd[i][j]) {
l = max(l, ll[i_][j]), r = max(r, rr[i_][j]);
x = i_ - i, y = r - l + 1;
if (x < n)
yy[x + 1] = min(yy[x + 1], y);
i_++;
}
x = i_ - i, y = 0;
if (x < n)
yy[x + 1] = min(yy[x + 1], y);
}
if (dd[i][j] == i) {
i_ = i, l = 0, r = m - 1;
while (i_ >= uu[i][j]) {
l = max(l, ll[i_][j]), r = max(r, rr[i_][j]);
x = i - i_, y = r - l + 1;
if (x < n)
yy[x + 1] = min(yy[x + 1], y);
i_--;
}
x = i - i_, y = 0;
if (x < n)
yy[x + 1] = min(yy[x + 1], y);
}
}
y = m, ans = 0;
for (x = 1; x <= n; x++) {
y = min(y, yy[x]);
ans = max(ans, x * y);
}
printf("%d\n", ans);
return 0;
}
