import java.util.*;
public class APP1{
    public static void main(String[] args){
        double sum=0.0;
        int n=0;
        int flag=1;
        int fm=1;
        Scanner reader =new Scanner(System.in);
        System.out.println("请输入n的值：");
        n=reader.nextInt();
        for(int i=0;i<=n;i++)
        {
            fm*=i;                  //阶乘
            sum+=(flag*1.0)/fm;
            flag=-flag;             //变号
        }
        System.out.println("sum的值为"+sum);
        }
}