import sys
input=lambda: sys.stdin.readline().rstrip()
n=int(input())
A=[int(i) for i in input().split()]
E,O=[0],[0]
for i in range(n):
  E.append(E[-1]+A[2*i])
  O.append(O[-1]+A[2*i+1])
eo=E[-1]
oo=O[-1]
ans=oo-eo
for i in range(n):
  ans=max(ans,oo-eo+2*E[i+1]-2*O[i+1])
print(ans)