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

def vsum(i,v):
    vlist = [0]*N
    while i < N:
        if i < 2:
            vlist[i] = V[i]
        elif i < 3:
            vlist[i] = vlist[i-2] + V[i]
        elif i < N:
            vlist[i] = max(vlist[i-2],vlist[i-3])+V[i]
        i += 1
    return vlist[N-1]

print(vsum(0,0))