import java.util.*;
public class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long N = sc.nextLong();
		long X = sc.nextLong();
		long T = sc.nextLong();
		long ans = N/X;
		if(N%X>0){
		    ans++;
		}
		System.out.println(ans*T);
	}
} import java.util.*; util.* java public class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long N = sc.nextLong();
		long X = sc.nextLong();
		long T = sc.nextLong();
		long ans = N/X;
		if(N%X>0){
		    ans++;
		}
		System.out.println(ans*T);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long N = sc.nextLong();
		long X = sc.nextLong();
		long T = sc.nextLong();
		long ans = N/X;
		if(N%X>0){
		    ans++;
		}
		System.out.println(ans*T);
	} main {
		Scanner sc = new Scanner(System.in);
		long N = sc.nextLong();
		long X = sc.nextLong();
		long T = sc.nextLong();
		long ans = N/X;
		if(N%X>0){
		    ans++;
		}
		System.out.println(ans*T);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) long N = sc.nextLong(); N sc.nextLong() sc.nextLong sc long X = sc.nextLong(); X sc.nextLong() sc.nextLong sc long T = sc.nextLong(); T sc.nextLong() sc.nextLong sc long ans = N/X; ans N/X N X if(N%X>0){
		    ans++;
		} N%X>0 N%X N X 0 {
		    ans++;
		} ans++ ans System.out.println(ans*T) System.out.println System.out System System.out ans*T ans T String[] args args public class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long N = sc.nextLong();
		long X = sc.nextLong();
		long T = sc.nextLong();
		long ans = N/X;
		if(N%X>0){
		    ans++;
		}
		System.out.println(ans*T);
	}
} public class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long N = sc.nextLong();
		long X = sc.nextLong();
		long T = sc.nextLong();
		long ans = N/X;
		if(N%X>0){
		    ans++;
		}
		System.out.println(ans*T);
	}
} Main
import java.util.*;
public class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long N = sc.nextLong();
		long X = sc.nextLong();
		long T = sc.nextLong();
		long ans = N/X;
		if(N%X>0){
		    ans++;
		}
		System.out.println(ans*T);
	}
}
