import sys
N = int(input())
V = [int(i) for i in input().strip().split(" ")]
K = [0 for i in range(N)]

K[0] = V[0]
if N == 1:
    print(K[0])
    sys.exit(0)

K[1] = max(V[0],V[1])
if N == 2:
    print(max(K[0],K[1]))
    sys.exit(0)

for i in range(2,N):
    K[i] = max(K[i-2]+V[i], K[i-1])

print(K[N-1])