Recursion+function

  // FACTORIAL NUMBER
import java.util.*;
public class Main
{
	public static void main(String[] args) {
	    Scanner sc = new Scanner(System.in);
	    int a =sc.nextInt();
	    int ans = fact(a);
	    System.out.print(ans);
		
	}
  public static int fact(int n)
	{
	    if(n==0){
	        return 1;
	    }
	    return n*fact(n-1);
	   
	}
	
}
    
    // FIBONACCI SERIES
import java.util.*;
public class Main
{
	public static void main(String[] args) {
	    Scanner sc = new Scanner(System.in);
	    int a =sc.nextInt();
	    int ans = fib(a);
	    System.out.print(ans);
		
	}
public static int fact(int n)
	{
	    
	   if(n==1){
	       return 0;
	       
	   }
	   if(n==2){
	       return 1;
	   }
	   return fib(n-1)+fib(n-2);
	  
	    
	}
	
}

// SUM OF DIGITS USING RECURSION
import java.util.*;
public class Main
{
	public static void main(String[] args) {
	    Scanner sc = new Scanner(System.in);
	    int a =sc.nextInt();
	    int ans = sum(a);
	    System.out.print(ans);
		
	}
public static int sum(int n)
	{
	    
	   if(n==0){
	       return 0;
	   }
	   return n%10 + sum(n/10);
	    
	}
	
}

// REVERSE AN ARRAY
import java.util.*;
public class Main
{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int a[] ={5, 4, 3, 2 ,1};
		reverse(a , 0 , a.length -1);
		System.out.print(Arrays.toString(a));
	}
	public static void reverse(int arr[], int start ,int end){
	    if(start>end){
	        return;
	    }
	    int temp = arr[start];
	    arr[start] = arr[end];
	    arr[end] = temp;
	    start++;
	    end--;
	    reverse(arr , start ,end);
	}
}