# 2次元dpだろう
# dp[i個目][食べない0、1食べる]おいしさ総和最大値

N = int(input())
V = [0]+list(map(int, input().split()))

dp = [[0]*2 for i in range(N+1)]

for i in range(1, N+1):
    v = V[i]
    # not eating
    dp[i][0] = max(dp[i-1][0], dp[i-1][1])
    # eating
    dp[i][1] = dp[i-1][0]+v
    
ans = max(dp[N])
print(ans)