Chemical Calculator

import java.util.Scanner;

public class Chemicals{

    public String chemical(int atomicNum){
        String[] abbrev = {"H", "He"};

        return abbrev[atomicNum-1];
    }

    private static double molarMass(int atomicNum){
        double[] amu = {1.008, 4.0026};

        return amu[atomicNum];
    }

    private static double calculator(){
        Scanner input;
        double sum = 0;
        int atomicNum = 0;
        input = new Scanner(System.in);
        int mols;
        while(atomicNum != -1){
            System.out.println("Enter atomic number of element, -1 to finish:");
            atomicNum = input.nextInt();
            if (atomicNum == -1){
                break;
            } else {
                System.out.println("Enter amount of element:");
                mols = input.nextInt();
                sum += (molarMass(atomicNum - 1) * mols); //This is an instance where the +=
                //operator is used. This adds the value of molarMass(atomicNum-1) * mols to the already existent
                //value of sum. 
            }
        }
        input.close();
        return sum;
    }

    public static void main(String[] args){
        double endValue = calculator();
        System.out.println(endValue + " amu");
        
    }
}
Chemicals.main(null);

Enter atomic number of element, -1 to finish:
Enter amount of element:
Enter atomic number of element, -1 to finish:
4.032 amu