import Foundation

let n = Int(readLine()!)!
let values = readLine()!.split(separator:" ").map { Int($0)! }
if n == 1 {
    print(values[0])
    exit(0)
}
var dp = Array<Int>(repeating: 0, count: 3)
dp[(n - 1) % 3] = values[n - 1];
dp[(n - 2) % 3] = Swift.max(values[n - 2], values[n - 1])
for i in (0 ..< n-2).reversed() {
    dp[i % 3] = Swift.max(values[i] + dp[(i + 2) % 3], dp[(i + 1) % 3])
}
print(dp[0])