N=int(input())

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

DP=[[0,0]for i in range(N+1)]

for i in range(1,N+1):
    DP[i][0]=max(DP[i-1])
    DP[i][1]=DP[i-1][0]+L[i]
print(max(DP[-1]))