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[2] = values[n - 1];
dp[1] = Swift.max(values[n - 2], values[n - 1])
for i in (0 ..< n-2).reversed() {
    let j = (i + 1002 - n) % 3
    dp[j] = Swift.max(values[i] + dp[(j + 2) % 3], dp[(j + 1) % 3])
}
print(dp[(1002 - n) % 3])