Factorial with a Loop

/*
 * Problem : Factorial.
 * Input   : One integer n.
 * Output  : n!.
 * Approach: A multiplication loop.
 * Time    : O(n)
 * Space   : O(1)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static long solve(long n) {
        // Step 1: Start with 1. This is also the answer for n = 0.
        long result = 1;

        // Step 2: Multiply by each number from 2 to n. 20! fits in a long (about 2.4 * 10^18).
        for (long i = 2; i <= n; i++) {
            result *= i;
        }
        return result;
    }

    public static void main(String[] args) {
        long n = new Scanner(System.in).nextLong();
        System.out.println(solve(n));
    }
}