big integer java

import java.math.BigInteger;// Java program to find large factorials using BigInteger 
import java.math.BigInteger; 
import java.util.Scanner; 
  
public class Example 
{ 
    // Returns Factorial of N 
    static BigInteger factorial(int N) 
    { 
        // Initialize result 
        BigInteger f = new BigInteger("1"); // Or BigInteger.ONE 
  
        // Multiply f with 2, 3, ...N 
        for (int i = 2; i <= N; i++) 
            f = f.multiply(BigInteger.valueOf(i)); 
  
        return f; 
    } 
  
    // Driver method 
    public static void main(String args[]) throws Exception 
    { 
        int N = 20; 
        System.out.println(factorial(N)); 
    } 
} 
import java.math.BigInteger;
BigInteger f = new BigInteger("1");