N = int(input())
V = list(map(int,input().split()))
V.extend([0,0,0])
value = 0
key = 0
for i in range(len(V)-2):
    if key == 2:
        key = 1
    elif key == 1:
        key = 0
    else:
        if V[i+1]+V[i+3] > V[i]+V[i+2] and V[i+1]+V[i+3] > V[i]+V[i+3]:
            value += V[i+1]
            key = 2
        else:
            value += V[i]
            key = 1
print(value)