source_code: 
  
  import java.io.PrintWriter;
  
  import java.util.*;
  import java.util.Arrays ; 
  import java .lang.String.* ;
  import java .lang.StringBuilder ;
  
  
  public class Test{
      static int pos = 0 ; 
      static int  arr[] ; 
    static LinkedList l1 = new  LinkedList() ; 
  static void find(int p ,char[]x,int put[],String s){
      int c= 0 ; 
      for (int i = 0; i < s.length(); i++) {
          if(x[p]==s.charAt(i)){
          c++ ; }
      }
      put[p] = c ;  
  }
  static int mode(int m ,int[]x ){
      int temp = 0 ; 
      for (int i = x.length-1; i >=0; i--) {
          if(x[i]<=m){
              temp= x[i] ; 
             /// break ; 
               return m-temp ; 
               
          }
      }
       return m-temp ; 
  }
  static int mode2(int m ,int[]x ){
      int temp = 0 ; 
      
      for (int i = x.length-1; i >=0; i--) {
          if(x[i]<=m){
              temp= x[i] ; 
             /// break ; 
               return x[i] ; 
               
          }
      }
       return 0 ; 
  }
  static int find(int x[],int temp){
      int j = 0 ; 
      for (int i = x.length-1; i >=0; i--) {
          if(x[i]==temp) return j+1 ; 
          j++ ; 
      }
      return -1 ; 
  }
  static String ch(long[]x,long b){
      for (int i = 0; i < x.length; i++) {
          if(x[i]==b)return "YES" ;
      }
      return "NO" ; 
  }
  
      public static void main(String[] args)  {
  
          Scanner in = new Scanner(System.in) ;
          PrintWriter pw = new PrintWriter(System.out);   
       int k=in.nextInt(), n=in.nextInt(), s=in.nextInt(), p=in.nextInt() ;
       int paper =n/s; 
       if(n%s!=0) paper++ ; 
       paper*=k ; 
       int fin = paper/p ; 
       if(paper%p!=0) fin++ ; 
          System.out.println( fin );
         
         
   }               
  }
  
  