#yuki999
n=int(input())
a=list(map(int,input().split()))
a1=a[::2]
a2=a[1::2]
sm=sum(a2)-sum(a1)
res=sm
for i in range(n):
 sm-=2*(a2[i]-a1[i])
 res=max(res,sm)
print(res)