N=gets.to_i
V=gets.split.map(&:to_i)

if N==1
    puts V[0]
    exit
end

if N==2
    puts [V[0],V[1]].max
    exit
end

DP=Array.new(N+1,0)
DP[1],DP[2]=V[0],V[1]

for i in 3..N do
    DP[i]=[DP[i-2],DP[i-3]].max+V[i-1]
end

puts [DP[N],DP[N-1]].max