let primLazy = 
    let odds = Seq.initInfinite (fun i -> 2 * i + 1)
    let rec f src =
        let (x, xs) = (Seq.head src, Seq.skip 1 src)
        seq {   
            yield x 
            for i in f xs do 
                if i % x <> 0 then yield i 
        }
    seq {   
        yield 2
        yield! f (Seq.skip 1 odds) 
    }

let N = stdin.ReadLine() |> int

primLazy
|> Seq.takeWhile(fun x -> x <= N)
|> Seq.sum
|> stdout.WriteLine