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

dp = [[0 for _ in range(2)] for _ in range(n+1)]
for i in range(n):
    dp[i+1][1]=dp[i][0] + v[i] # eat
    dp[i+1][0]=max(dp[i][0],dp[i][1]) # pass

print(max(dp[-1]))