@[reducible] def Map : Type := RBMap Nat Bool (fun a b => a < b)

def mkMapAux : Nat → Map → Map
| 0, m => m
| n+1,   m => mkMapAux n (m.insert n (n % 10 = 0))

def mkMap (n : Nat) :=
mkMapAux n {}

def main (xs : List String) : IO UInt32 :=
let m := mkMap xs.head.toNat;
let v := m.fold (fun (r : Nat) (k : Nat) (v : Bool) => if v then r + 1 else r) 0;
IO.println (toString v) *>
pure 0