H,W = gets.split().map(&:to_i)
a = []

H.times do |i|
	if i == 0
		a[i] = gets.split().map{|c| c == "0" ? 1 : 0}
	else
		a[i] = gets.split().map.with_index do |c, j|
			c == "0" ? a[i-1][j]+1 : 0
		end
	end
	a[i] << 0
end

r = 0

H.times do |i|
	s = [[0,0]]
	(W+1).times do |j|
		c = a[i][j]
		if c > s[-1][0]
			s << [c,j]
		else
			while c < s[-1][0] do
				h, sj = s.pop
				q = h * (j-sj)
				r = q if q > r
			end
		end
	end
end
p r