from collections import deque
def func(v1,arg1):
    sum1 = 0
    for num2 in range(1,n+1):
        if(arg[num2] is True):
            sum1 += v1[num2]
    return sum1

n = int(input())
m = input().split()
v = [0]
sum = []
for num in range(n):
    v.append(int(m[num]))
q = deque([])
arg = [False]
for num3 in range(n):
    if num3 % 2 != 1:
        arg.append(True)
        q.append(num3)
    else:
        arg.append(False)
sum.append(func(v,arg))
while len(q) > 0:
    a = q.pop()
    for num4 in range(a,n+1):
        if (a+num4) % 2 == 0:
            arg[num4] = False
        else:
            arg[num4] = True
            q.append(num4)
    sum.append(func(v,arg))
print(max(sum))