I need this program be able to handle invalid input -- (negative numbers, symbols, etc. anythng else but positive integer)

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import java.util.Scanner;

public class Recursion {

public static void main(String[] args) {

int factorial;

System.out.println("Enter a positive integer");

Scanner sc=new Scanner(System.in);

int n=sc.nextInt();

Recursion f=new Recursion();

factorial=f.fact(n);

System.out.println("The product of the numbers from 1 to "+n+" "+"("+n+") is: "+factorial);

int sum=f.sum(n);

System.out.println("The sum is: "+sum);

int fibonacci =f.fibonacci(n);

System.out.println("The "+n+"th Fibonacci number is: "+fibonacci);

}

int fibonacci(int n) {

if (n <= 1)

return n;

return fibonacci(n-1) + fibonacci(n-2);

}

int sum(int n) {

if (n == 1)

return 1;

else

return n + sum(n-1);

}

int fact(int x) {

if(x > 1)

{

return(x * fact(x - 1));

}

return 1;

}

}