source_code: import java.util.*;
  public class Main {
  
      public static void main(String args[]) {
          Scanner scan = new Scanner(System.in);
          int n=scan.nextInt();
          int m=scan.nextInt();
          int[] game=new int[n];
          int[] bill=new int[m];
          for (int i = 0; i <n ; i++) {
              game[i]=scan.nextInt();
          }
          for (int i = 0; i <m ; i++) {
              bill[i]=scan.nextInt();
          }
          int i=0;
          int j=0;
          int ans=0;
          while (i<m){
              boolean f=true;
              for (int k = j; k <n ; k++) {
                  if (bill[i]>=game[k]){
                      ans++;
                      i++;
                      j=k+1;
                      f=false;
                      break;
                  }
              }
              if (f){
                  break;
              }
          }
          System.out.println(ans);
      }
  }
  
  
  