import copy

n = int(input())
v = [int(x) for x in input().split()]
p = [0 for _ in range(n)]

if n==1:
    p[0] = v[0]
else:
    p[0] = v[0]
    p[1] = max(v[0],v[1])
    for i in range(2,n):
        p[i] = max(p[i-1],p[i-2]+v[i])

print(p[n-1])