N = int(input())
V = list(map(int,input().split()))
p0 = 0
p1 = 0
q0 = 0
q1 = 0
for i in range(len(V)):
    p1 = V[i] + q0
    q1 = max(p0,q0)
    p0 = p1
    q0 = q1
print(max(p1,q1))