N = int(input())
A = list(map(int,input().split()))
DP = [[0] * (N+1) for i in range(2)]
for i in range(1,N+1):
    DP[0][i] = max(DP[0][i-1],DP[1][i-1])
    DP[1][i] = DP[0][i-1]+A[i-1]
print(max(max(DP[0]),max(DP[1])))