Giai thừa - java

package baitap;
import java.util.Scanner;
public class baitap {
public static int n;
    //---------ham tinh giai thua--------------
    public static double giaithua(int n){
        double tmp = 1;
        if (n>1) {
            for (int i = 2; i <= n; i++) {
                tmp *= i;
            }
        }
        return tmp;
    }
    /**
    * @param args the command line arguments
    * S = 1/1! + 1/2! + 1/3! + ... + 1/n!
    */
    public static void main(String[] args) {
        // TODO code application logic here
        float tong = 0.0f;
        Scanner reader = new Scanner(System.in);
        System.out.print("Nhap so tu nhien N = ");
        n = reader.nextInt();
        for (int i = 1; i <= n; i++) {
            tong += 1/giaithua(i);
        }
        System.out.println("tong day so la: " + tong);
    }
}