I need to create a program that uses while to find the volume of a cylinder. I need the while loop to break if the user inputs a negative value for the height. My code looks like this:

double sentinel=1, h=1, v=0, r, count=0; // declares all variables needed
    final double PI=3.14159;
    boolean NotNegative=true;

while(NotNegative){// && count==0){ // while both the height is positive AND the total times run is 0
        System.out.print("Enter height (Use negative to exit): "); // has the user input the height
        h=Double.parseDouble(br.readLine());
        sentinel=h; // save sentinel as the inputted height

        while(sentinel>0){

           System.out.print("Enter radius: "); // have the user input the radius
           r=Double.parseDouble(br.readLine());
           v=PI*(r*r)*h; // find the volume
           System.out.println("The volume is " + v); // print out the volume
           count++; // increase the count each time this runs
           NotNegative=true;
           sentinel=-1;
        }
    }   

Any help?