import Foundation
func toTuple<T>(_ args: [T]) -> (T, T, T) { (args[0], args[1], args[2]) }
func readInts() -> [Int] { readLine()!.split(separator: " ").map { Int($0)! } }

let (n, x, t) = toTuple(readInts())
var ans = n / x * t
if n % x != 0 {
  ans += t
}
print(ans)