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

def max_score(N, w_list):
    score_list=[0]*(N+1)
    score_list[1]=w_list[1]
    if N<2:
        return w_list[1]
    if w_list[1]>w_list[2]:
        score_list[2]=w_list[1]
    else:
        score_list[2]=w_list[2]
        
    for i in range(3, N+1):
        score1=score_list[i-2]+w_list[i]
        score2=score_list[i-1]
        if score1>score2:
            score_list[i]=score1
        else:
            score_list[i]=score2
            
    return score_list[N]
    
print(max_score(N, w_list))