package test;

import java.math.BigInteger;

public class Test {

    public static void main(String[] args) {

        new Test().run();
    }
    void run(){
        System.out.println("normal factorial: " +fact(50));
        System.out.println("tail factorial: " +fact_tail(1, 50));



    public long fact_tail(long product, long target ){
        if (target == 1) return product;
        return fact_tail(product* target, target - 1);
    }

    public long fact(int n){
if (n < 1) return n;
return n* fact(n-1);
    }


}