# coding: utf-8
# Your code here!
N=int(input())
A=list(map(int,input().split()))

fro=[A[2*i]-A[2*i+1] for i in range(N)]
back=[-A[2*i]+A[2*i+1] for i in range(N)]

temp=sum(fro)
ans=temp
for i in range(N)[::-1]:
    temp+=back[i]-fro[i]
    ans=max(ans,temp)
    
print(ans)