import java.util.Scanner;
class Test {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("请输入一个整数:");
int n = sc.nextInt();
double sum=0;
if(n%2==0){
for(int i=2;i<=n;i+=2){
double a = (double)1/i;
sum+=a;
}
}else{
for(int i=1;i<=n;i+=2){
double a = (double)1/i;
sum+=a;
}
}
System.out.println(sum);
}
}
