N = gets.to_i
a = gets.split(" ").map{|s| s.to_i}

sum = [0]
0.upto(N-1) {|i|
	sum << sum[-1] + a[2*i] - a[2*i+1]
}

rsum = 0
max = sum[-1]
(N-1).downto(0) {|i|
	rsum += a[2*i+1] - a[2*i]
	val = rsum + sum[i]
	max = val if max < val
}

puts max