readLine() fejl!

har denne kode....

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import java.io.*;

public class TelephoneBill {
    static BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));

    public static void main (String[]args) {
        try {
            System.out.println("Telephone Bill Calculation");

            // constant values
            final double standingCharge = 18.00; // 18 pounds/quarter
            final double unitCharge = 0.0375; // 3.75 pence/unit

            int unitsUsed, pounds, pence;
            double totalCharge;

            // input number of units used
            System.out.print("Enter number of units used: ");
            unitsUsed = stdin.readLine();

            // calculate charge
            totalCharge = standingCharge + unitsUsed * unitCharge;

            // convert to punds and pence
            pounds = (int) totalCharge;
            pence = (int) ( ( totalCharge - pounds ) * 100 );

            // output charges
            System.out.print(unitsUsed);
            System.out.println(" units used");
            System.out.print("total bill = ");
            System.out.print(pounds + "." + pence);
        }
        catch(Exception e) {
            e.printStackTrace();
        }

    } // main

}

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og denne fejl kommer når jeg compiler...

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C:\Documents and Settings\Carsten Risager\Skrivebord\Programmering\Java\Java\TelephoneBill.java:19: incompatible types
found  : java.lang.String
required: int
            unitsUsed = stdin.readLine();
                                                  ^
1 error

Tool completed with exit code 1

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hvad gør jeg galt? nogen?

//WebPsycho