#include <bits/stdc++.h>
int main() {
  int n, x, t, tmp;
  tmp = scanf("%d", &n);
  tmp = scanf("%d", &x);
  tmp = scanf("%d", &t);
  printf("%d\n", (n % x == 0) ? t * (n / x) : t * ((n / x) + 1));
  return 0;
}
