/*No.143 豆*/ import java.util.*; public class No143 { public static void main(String[] args) { byte family,age_eat=0; short tsubu,fukuro; int mame; try(Scanner input = new Scanner(System.in)){ tsubu=input.nextShort(); fukuro=input.nextShort(); family=input.nextByte(); byte age[]=new byte[family]; for(byte i=0;iage[j]){ mame-=age[j]; age_eat++; } } if(age_eat==0){ System.out.println(-1); }else{ System.out.println(mame); } }catch(Exception e){ e.printStackTrace(); } } }