java，

java，

package Array;

import java.util.Scanner;

public class Demo7 {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner sc =new Scanner(System.in);
int n=sc.nextInt();
double sum=0.0;

for (int j = 1; j <=n; j++) {
int sub=1;
for (int i = 1; i <=j; i++) {
sub=sub*i;
}
if(j%2==0){
sum=sum-1.0/sub;
}

if(j%2!=0){
sum=sum+1.0/sub;
}

}

System.out.println(sum);
}
}