import sys
n=int(input())
v=list(map(int,input().split()))
if n<3:
    print(max(v))
    sys.exit()
table=[0]*(n)
table[0]=v[0]
table[1]=v[1]
table[2]=v[0]+v[2]
for i in range(3,n):
    table[i]=v[i]+max(table[i-2],table[i-3])
print(max(table))