// #pragma GCC optimize("Ofast,no-stack-protector")
// #pragma GCC optimize("O3,unroll-loops")
// #pragma GCC target("avx,avx2,bmi,bmi2,lzcnt,popcnt")
#include <bits/stdc++.h>
#define lowbit(x) ((x) & -(x))
#define ml(a, b) ((1ll * (a) * (b)) % M)
#define tml(a, b) (a) = ((1ll * (a) * (b)) % M)
#define ad(a, b) ((0ll + (a) + (b)) % M)
#define tad(a, b) (a) = ((0ll + (a) + (b)) % M)
#define mi(a, b) ((0ll + M + (a) - (b)) % M)
#define tmi(a, b) (a) = ((0ll + M + (a) - (b)) % M)
#define tmin(a, b) (a) = min((a), (b))
#define tmax(a, b) (a) = max((a), (b))
#define iter(a) (a).begin(), (a).end()
#define riter(a) (a).rbegin(), (a).rend()
#define init(a, b) memset((a), (b), sizeof(a))
#define cpy(a, b) memcpy((a), (b), sizeof(a))
#define uni(a) a.resize(unique(iter(a)) - a.begin())
#define size(x) (int)x.size()
#define pb emplace_back
#define mpr make_pair
#define ls(i) ((i) << 1)
#define rs(i) ((i) << 1 | 1)
#define INF 0x3f3f3f3f
#define NIF 0xc0c0c0c0
#define eps 1e-9
#define F first
#define S second
#define AC cin.tie(0)->sync_with_stdio(0)
using namespace std;
typedef long long llt;
typedef __int128_t lll;
typedef pair<int, int> pii;
typedef pair<double, double> pdd;
typedef pair<llt, llt> pll;
typedef complex<double> cd;
// const int M = 998244353;
// random_device rm;
// mt19937 rg(rm());
// default_random_engine rg(rm());
// uniform_int_distribution<int> rd(INT_MIN, INT_MAX);
// uniform_real_distribution<double> rd(0, M_PI);
void db() { cerr << "\n"; }
template <class T, class... U>
void db(T a, U... b) { cerr << a << " ", db(b...); }
inline char gc()
{
const static int SZ = 1 << 16;
static char buf[SZ], *p1, *p2;
if (p1 == p2 && (p2 = buf + fread(p1 = buf, 1, SZ, stdin), p1 == p2))
return -1;
return *p1++;
}
void rd() {}
template <typename T, typename... U>
void rd(T &x, U &...y)
{
x = 0;
bool f = 0;
char c = gc();
while (!isdigit(c))
f ^= !(c ^ 45), c = gc();
while (isdigit(c))
x = (x << 1) + (x << 3) + (c ^ 48), c = gc();
f && (x = -x), rd(y...);
}
template <typename T>
void prt(T x)
{
if (x < 0)
putchar('-'), x = -x;
if (x > 9)
prt(x / 10);
putchar((x % 10) ^ 48);
}
const int N = 2505;
char gd[N][N];
int up[N][N], dn[N][N], an[N];
signed main()
{
int n, m;
scanf("%d%d", &n, &m);
for (int i = 1; i <= n; i++)
scanf("%s", gd[i] + 1);
bool ok = 0;
for (int j = 1; j <= m; j++)
{
for (int i = 1; i <= n; i++)
if (gd[i][j] == '1')
up[i][j] = up[i - 1][j] + 1;
for (int i = n; i > 0; i--)
if (gd[i][j] == '1')
dn[i][j] = dn[i + 1][j] + 1, ok = 1;
}
assert(ok);
init(an, INF);
int mx = m;
for (int i = 1; i <= n; i++)
{
int m1 = INF, m2 = INF, cr = 0;
for (int j = 1; j <= m; j++)
{
if (gd[i][j] == '0')
{
m1 = m2 = INF;
if (cr)
tmin(mx, cr), cr = 0;
continue;
}
cr++, tmin(m1, up[i][j]), tmin(m2, dn[i][j]);
tmin(an[cr], m1 + m2 - 1);
tmin(an[1], up[i][j] + dn[i][j] - 1);
}
for (int j = m; j > 0; j--)
{
if (gd[i][j] == '0')
{
m1 = m2 = INF;
if (cr)
tmin(mx, cr), cr = 0;
continue;
}
cr++, tmin(m1, up[i][j]), tmin(m2, dn[i][j]);
tmin(an[cr], m1 + m2 - 1);
tmin(an[1], up[i][j] + dn[i][j] - 1);
}
}
int ans = 0;
for (int i = 1; i <= mx; i++)
tmax(ans, an[i] * i), tmin(an[i + 1], an[i]);
prt(ans), putchar('\n');
}
