n = int(input())
V = list(map(int,input().split()))

if n == 1:
    print(V[0])
    exit()

dp = [0]*n
dp[0] = V[0]
dp[1] = max(V[0], V[1])
for i in range(2,n):
    dp[i] = max(dp[i-1], dp[i-2]+V[i])

print(dp[n-1])