import Foundation

let n = Int(readLine()!)!
let values = readLine()!.split(separator:" ").map { Int($0)! }
if n == 1 {
    print(values[0])
    exit(0)
}
if n == 2 {
    print(values.max()!)
    exit(0)
}

var dp = Array<Int>(repeating: -1, count: n)
dp[n - 1] = values[n - 1];
dp[n - 2] = Swift.max(values[n - 2], values[n - 1])
for i in (0 ..< n-2).reversed() {
    dp[i] = Swift.max(values[i] + dp[i + 2], dp[i + 1])
}

print(dp[0])