n=gets.to_i
xs=gets.split(" ").map{|e| e.to_i}
ls=[0]
rs=[0]
s=0
n.times{|i|
	s+=xs[i*2]-xs[i*2+1]
	ls<<s
}
s=0
(n-1).downto(0){|i|
	s+=xs[i*2+1]-xs[i*2]
	rs.unshift(s)
}
ans=ls[0]+rs[0]
0.upto(n){|i|
	ans=[ans,ls[i]+rs[i]].max
}
puts ans