import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    long b1 = sc.nextLong();
    long b2 = sc.nextLong();
    long b3 = sc.nextLong();
    long ans = (long)((b2 * b3 - b3 * b3 - b2 * b2 + b1 * b3) / (b1 - b2));
    System.out.println(ans);
  }
}