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

A.insert(0,0)

X = 0
Y = 0
MaxT = [0, A[1]]
MaxD = [0, 0, A[1]]

if N == 1:
    print(A[1])
    exit()
else:
    MaxT.append(A[2])
    for i in range (3, N+1):
        X = max(MaxT[i-2], MaxD[i-2]) + A[i]
        Y = max(MaxD[i-2] + A[i-1], MaxT[i-2])
        MaxT.append(X)
        MaxD.append(Y)
        
if MaxT[N] >= MaxD[N]:
    print(MaxT[N])
else:
    print(MaxD[N])