I faced trouble and I can't do anything with that. I wonder how may I call this method? 

```
public static BigInteger factorial(BigInteger n) {
    BigInteger result = BigInteger.ONE;

    while (!n.equals(BigInteger.ZERO)) {
        result = result.multiply(n);
        n = n.subtract(BigInteger.ONE);
    }

    return result;
}

```

For var=1, I got it, I wrote following: 

```
BigInteger kk = BigInteger.ONE;
System.out.println(factorial(kk));

```

but, I confused how to count 61!, for instance.