I have an issue with stopping the process at a negative number

Mass and Weight 
Scientists measure an object’s mass in kilograms and its weight in newtons. If you know
the amount of mass that an object has, you can calculate its weight, in newtons, with
the following formula:  Weight = mass * 9.8  Write a program that asks the user to enter an object’s mass, and then calculates and
displays its weight. If the object weighs more than 1,000 newtons, display a message
indicating that it is too heavy. If the object weighs less than 10 newtons, display a mes-
sage indicating that the object is too light. The program will continue until a negative number is entered for the mass.

#include <iostream>
using namespace std;

int main()
{
double mass, weight;
do
{
   cout << "Enter the object's mass (in kilograms).  A negative mass stops the program.";
cin>>mass;

weight = (mass*9.8);
 cout << "The object weighs " << weight
        << " Newtons.\n";

if(weight>1000){

    cout << "The object is too heavy!\n";
}


else if(weight<10){

      cout << "The object is too light!\n";
}



}while(weight>=0);

   return 0;
}