型別：模擬
題意：從地球起飛->星球1降落->星球1起飛->星球2起飛->······->星球n-1起飛->地球降落
題解：逆過程模擬，如果費用存在<=1的就直接輸出-1

import java.util.Scanner;

public class C {
    public static void main(String[] args) {
        Scanner kb = new Scanner(System.in);
        int n=kb.nextInt();
        double sum=kb.nextDouble();
        double
 
 sum1=0;
        double aa;
        double a[]=new double[n];
        double b[]=new double[n];
        boolean pd=false;
        for(int i=0;i<n;i++) {
            a[i]=kb.nextDouble();
            if(a[i]<1.1)pd=true;
        }
        for(int i=0;i<n;i++) {
            b[i]=kb.nextDouble();
            if
 
(b[i]<1.1)pd=true;
        }
        if(pd) {
            System.out.println(-1);
            return;
        }
        aa=sum/(b[0]-1);
        sum1+=aa;
        sum+=aa;
        for(int i=n-1;i>0;i--) {
            aa=sum/(a[i]-1);
            sum1+=aa;
            sum+=aa;
            aa=sum/(b[i]-1
 
);
            sum1+=aa;
            sum+=aa;
        }
        aa=sum/(a[0]-1);
        sum1+=aa;
        sum+=aa;
        System.out.println(sum1);
        kb.close();
    }
}