N = int(input())
A = list(map(int,input().split()))
B = [a-b for a,b in zip(A[::2], A[1::2])]
C = [0]
for b in B:
    C.append(C[-1] + b)
D = [0]
for b in reversed(B):
    D.append(D[-1] - b)
D.reverse()
ans = 0
for c,d in zip(C,D):
    ans = max(ans, c+d)
print(ans)