import java.util.*; public class Main { public static void main(String[] args){ Scanner sc = new Scanner(System.in); int k = sc.nextInt(); int n = sc.nextInt(); int mame = k*n; int f = sc.nextInt(); int sum = 0; for(int i=0;isum){ System.out.println(mame-sum); }else{ System.out.println(-1); } } }