import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; public class Main { public static void main(String[] args) throws IOException { proconScan proScan = new proconScan(" "); proScan.scan(); Integer numK = proScan.nextInt(); Integer numN = proScan.nextInt(); //Integer numF = proScan.nextInt(); proScan.scan(); Integer sum = 0; for (Integer buf : proScan.getInt()) { sum += buf; } Integer buf = numK * numN; if(buf>sum){ System.out.print(buf-sum); }else{ System.out.print("-1"); } proScan.proconEnd(); } } class proconScan { private BufferedReader br; private String inLine; private String[] inString; private Integer idx; private String splitChar; public proconScan() { br = new BufferedReader(new InputStreamReader(System.in)); idx = 0; splitChar = " "; } public proconScan(String split) { br = new BufferedReader(new InputStreamReader(System.in)); idx = 0; splitChar = split; } public void proconEnd() throws IOException { // TODO 自動生成されたメソッド・スタブ br.close(); } public String scan() throws IOException { idx = 0; inLine = br.readLine(); inString = inLine.split(splitChar, 0); return inLine; } public Integer scanInteger1() throws IOException { scan(); return Integer.parseInt(inString[0]); } public String backLine() { return inLine; } public String nextString() { return inString[idx++]; } public String[] getString() { return inString; } public Integer nextInt() { Integer num; try { num = Integer.parseInt(inString[idx++]); } catch (NumberFormatException e) { num = null;// TODO: handle exception } return num; } public Integer[] getInt() { Integer[] num = new Integer[this.getLen()]; for (int i = 0; i < this.getLen(); i++) { num[i] = Integer.parseInt(inString[i]); } return num; } public Float nextFloat() { Float num; try { num = Float.parseFloat(inString[idx++]); } catch (NumberFormatException e) { num = null;// TODO: handle exception } return num; } public Float[] getFloat() { Float[] num = new Float[this.getLen()]; for (int i = 0; i < this.getLen(); i++) { num[i] = Float.parseFloat(inString[i]); } return num; } public Integer getLen() { return inString.length; } }