#include <algorithm>
#include <cstdio>
int st[2005], len[2005]; 
char str[2005][2005]; 
int main()
{
	// freopen("ARC081-F.in", "r", stdin); 
	int n, m; 
	scanf("%d%d", &n, &m);  
	for (int i = 0; i < n; i++)
		scanf("%s", str[i]); 
	int ans = std::max(n, m);
	for (int i = 0; i < n; i++)
	{
		for (int j = 0; j < m - 1; j++)
		{
			if (i && !(str[i - 1][j] ^ str[i][j] ^ str[i - 1][j + 1] ^ str[i][j + 1]))
				len[j]++; 
			else
				len[j] = 1; 
		}
		int tp = 0; 
		for (int j = 0; j < m; j++)
		{
			while (tp && len[st[tp - 1]] >= len[j])
			{
				int x = st[--tp]; 
				if (!tp)
					ans = std::max(ans, (j + 1) * len[x]); 
				else
					ans = std::max(ans, (j - st[tp - 1]) * len[x]); 
			}
			st[tp++] = j; 
		}
	}
	printf("%d\n", ans);
	return 0; 
}
