[BaekJoon] #27433 팩토리얼2

import java.util.*;
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		System.out.println(factorial(N));
	}
	
	public static long factorial(int n) {
		if(n == 0) return 1;
		return n * factorial(n - 1);
	}
}

factorial를 long형으로 정의해야한다!