import java.io.*; class no143 { public static void main(String args[])throws IOException { BufferedReader sc=new BufferedReader(new InputStreamReader(System.in)); String knf[]=sc.readLine().split(" "); String a[]=sc.readLine().split(" "); int k,n,f,req=0; k=Integer.parseInt(knf[0]); n=Integer.parseInt(knf[1]); f=Integer.parseInt(knf[2]); for(int i=0;i0)System.out.println(k*n-req); else System.out.println(-1); } }