n=int(input())
a=[*map(int,input().split())]
r=[0]*(len(a)//2)
l=[0]*(len(a)//2)
rn,ln=0,0
for i in range(len(a)//2):
    rn+=a[2*i]-a[2*i+1]
    ln+=a[2*(n-i)-1]-a[2*(n-i-1)]
    r[i]=rn
    l[-i-1]=ln
rn=0
for i in range(len(r)-1):
    rn=max(rn,r[i]+l[i+1])
print(rn)