n, m = gets.split(" ").map{|s| s.to_i}

a = []

n.times {
	a << gets.split(" ").map{|s| s.to_i}.sum
}

dp = Array.new(n+1) {Array.new(n+1, -Float::INFINITY)}

dp[0][0] = 0

1.upto(n) {|i|
	dp[i][0] = 0
	1.upto(n) {|j|
		dp[i][j] = [dp[i-1][j], dp[i-1][j-1] + (j % 2 == 1 ? a[i-1] : -a[i-1])].max
	}
}

puts dp[n].max