import java.util.*;

public class Exercise38{
  public static void main (String[] args){

    Scanner sc = new Scanner(System.in);

    int num = sc.nextInt();
    ArrayList<Integer> array = new ArrayList<Integer>();

    for (int n = 0; n < num; n++){
      array.add(sc.nextInt());
    }

    int count = 0;

    int index = 1;

    while (index < array.size()){
      if (array.get(index) - array.get(index - 1) > 1){
        count++;
      }  
      if (array.get(index - 1) > array.get(index)){
        count++;
        array.remove(index);
        continue;
      }
      index++;
    }

    System.out.println(count);
  }
}