n = int(input())
a = list(map(int, input().split()))
dp = [a[0]]
if n >= 2:
    dp.append(a[1])
for i in range(2, n):
    if dp[i-1] + a[i] < dp[i-2] + a[i]:
        dp.append(dp[i-1] + a[i])
    else:
        dp.append(dp[i-2] + a[i])

print(dp[-1])