let ``No.51 やる気の問題`` () =
    let W = stdin.ReadLine() |> int |> bigint
    let D = stdin.ReadLine() |> int |> bigint
    seq [ D..(-1I)..1I ]
    |> Seq.take (int D - 1)
    |> Seq.fold (fun s n -> s - (s/(n*n))) W
    |> int
    |> printfn "%d"
``No.51 やる気の問題`` ()