#define MAX_NM 200

#include <iostream>

#include <fstream>
using namespace std;

ifstream fin("bmatrix.in");
ofstream fout("bmatrix.out");

int n, m;
bool A[MAX_NM + 2][MAX_NM + 2];

int indMaxL[MAX_NM + 2][MAX_NM + 2], indMaxR[MAX_NM + 2][MAX_NM + 2];
int MRL[MAX_NM + 2][MAX_NM + 2], MRR[MAX_NM + 2][MAX_NM + 2];

int VMAL[MAX_NM + 2], VMAR[MAX_NM + 2];
int HMAU[MAX_NM + 2], HMAD[MAX_NM + 2];

int main()
{
	fin >> n >> m;
	
	char aux[MAX_NM + 1];
	for (int i = 1; i <= n; ++i)
	{
		fin >> (aux + 1);
		
		for (int j = 1; j <= m; ++j)
		{
			if (aux[j] == '0')
			{
				A[i][j] = false;
			}
			else
			{
				A[i][j] = true;
			}
		}
	}
	
	for (int i = 1; i <= n; ++i)
	{
		for (int j = 1; j <= m; ++j)
		{	
			if (A[i][j])
			{
				indMaxL[i][j] = j;
			}
			else
			{	
				indMaxL[i][j] = indMaxL[i][j - 1];
			}
		}
	}
	
	for (int i = 1; i <= n; ++i)
	{
		indMaxR[i][m + 1] = m + 1;
	}
	
	for (int i = 1; i <= n; ++i)
	{	
		for (int j = m; j >= 1; --j)
		{
			if (A[i][j])
			{
				indMaxR[i][j] = j;
			}
			else
			{
				indMaxR[i][j] = indMaxR[i][j + 1];
			}
		}
	}
	
	for (int i = 1; i <= n; ++i)
	{
		for (int j = 1; j <= m; ++j)
		{
			int maLeft = 0;
			
			for (int w = 1; w <= i; ++w)
			{
				if (A[i - w + 1][j])
				{
					break;
				}
				
				if (maLeft < indMaxL[i - w + 1][j])
				{
					maLeft = indMaxL[i - w + 1][j];
				}
				
				if (MRL[i][j] < ((j - maLeft) * w))
				{
					MRL[i][j] = (j - maLeft) * w;
				}
			}
		}
	}
	
	for (int i = 1; i <= n; ++i)
	{
		for (int j = 1; j <= m; ++j)
		{
			int maRight = m + 1;
			
			for (int w = 1; w <= (n - i + 1); ++w)
			{
				if (A[i + w - 1][j])
				{
					break;
				}
				
				if (maRight > indMaxR[i + w - 1][j])
				{
					maRight = indMaxR[i + w - 1][j];
				}
				
				if (MRR[i][j] < ((maRight - j) * w))
				{
					MRR[i][j] = (maRight - j) * w;
				}
			}
		}
	}
	
	for (int i = 1; i <= n; ++i)
	{
		HMAU[i] = HMAU[i - 1];
		
		for (int j = 1; j <= m; ++j)
		{
			if (HMAU[i] < MRL[i][j])
			{
				HMAU[i] = MRL[i][j];
			}
		}
	}
	
	for (int i = 1; i <= n; ++i)
	{
		HMAD[i] = HMAD[i + 1];
		
		for (int j = 1; j <= m; ++j)
		{
			if (HMAD[i] < MRR[i][j])
			{
				HMAD[i] = MRR[i][j];
			}
		}
	}
	
	for (int j = 1; j <= m; ++j)
	{
		VMAL[j] = VMAL[j - 1];
		
		for (int i = 1; i <= n; ++i)
		{
			if (VMAL[j] < MRL[i][j])
			{
				VMAL[j] = MRL[i][j];
			}
		}
	}
	
	for (int j = 1; j <= m; ++j)
	{
		VMAR[j] = VMAR[j + 1];
		
		for (int i = 1; i <= n; ++i)
		{
			if (VMAR[j] < MRR[i][j])
			{
				VMAR[j] = MRR[i][j];
			}
		}
	}
	
	int rasp = 0;
	
	for (int j = 1; j < m; ++j)
	{
		if (rasp < (VMAL[j] + VMAR[j + 1]))
		{
			rasp = VMAL[j] + VMAR[j + 1];
		}
	}
	
	for (int i = 1; i < n; ++i)
	{
		if (rasp < (HMAU[i] + HMAD[i + 1]))
		{
			rasp = HMAU[i] + HMAD[i + 1];
		}
	}
	
	fout << rasp;
	
	fin.close();
	fout.close();
	return 0;
}