n=int(input())
v=[int(i) for i in input().split()]
if len(v)>1:
    if v[0]>v[1]:v[1]=v[0]
for i in range(2,n):
    v[i]=(v[i]+v[i-2] if v[i-1]<v[i-2]+v[i] else v[i-1])
print(max(v))