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

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

print(max(dp[n]))