source_code: 
  import java.util.*;
  import java.io.*;
  import java.math.*;
  public class loser
  {
      static class InputReader {
          public BufferedReader br;
          public StringTokenizer token;
          public InputReader(InputStream stream)
          {
              br=new BufferedReader(new InputStreamReader(stream),32768);
              token=null;
          }
  
          public String next()
          {
              while(token==null || !token.hasMoreTokens())
              {
                  try
                  {
                      token=new StringTokenizer(br.readLine());
                  }
                  catch(IOException e)
                  {
                      throw new RuntimeException(e);
                  }
              }
              return token.nextToken();
          }
  
          public int nextInt()
          {
              return Integer.parseInt(next());
          }
  
          public long nextLong()
          {
              return Long.parseLong(next());
          }
      }
      static class card{
          long a;
          int i;
          public card(long a,int i)
          {
              this.a=a;
              this.i=i;
          }
      }
      static class sort implements Comparator<pair>
      {
          public int compare(pair o1,pair o2)
          {
              if(o1.a!=o2.a)
                  return (int)(o1.a-o2.a);
              else
                  return (int)(o1.b-o2.b);
          }
      }
      static void shuffle(long a[])
      {
          List<Long> l=new ArrayList<>();
          for(int i=0;i<a.length;i++)
              l.add(a[i]);
          Collections.shuffle(l);
          for(int i=0;i<a.length;i++)
              a[i]=l.get(i);
      }
  
      /*static long gcd(long a,long b)
      {
      if(b==0)
      return a;
      else
      return gcd(b,a%b);
      }*/
      /*static boolean valid(int i,int j)
      {
      if(i<4 && i>=0 && j<4 && j>=0)
      return true;
      else
      return false;
      }*/
      static class pair{
          int a,b;
          public pair(int a,int b)
          {
              this.a=a;
              this.b=b;
          }
      }
      public  static void main(String[] args) 
      {
          InputReader sc=new InputReader(System.in);
          int k=sc.nextInt();
          int n=sc.nextInt();
          int s=sc.nextInt();
          int p=sc.nextInt();
          long d=(long)Math.ceil((double)n/s);
          if(d==0)
          d=1;
          d=k*d;
          long ans=(long)Math.ceil((double)d/p);
          System.out.println(ans);
      }
  }