import java.util.*;
public class Test10 {
  public static void main(String[] args){
    Scanner sc=new Scanner(System.in);
    String line;
    line=sc.nextLine();
    int n=Integer.parseInt(line);
    int[] cups=new int[n+1];
    for(int i=0;i<n;i++){
      line=sc.nextLine();
      cups[i]=Integer.parseInt(line);
    }
    cups[n]=Integer.MAX_VALUE;
    Arrays.sort(cups);
    int max=0;
    while(cups[0]<Integer.MAX_VALUE){
      max++;
      int tmp=0;
      for(int i=0;cups[i]<Integer.MAX_VALUE;i++){
        if(tmp<cups[i]){
          tmp=cups[i]+1;
          cups[i]=Integer.MAX_VALUE;
        }
      }
      Arrays.sort(cups);
    }
    System.out.println(max);
    sc.close();
  }
}