import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long b1 = sc.nextInt();
        long b2 = sc.nextInt();
        long b3 = sc.nextInt();
        long b4 = (b3 * (b2 - b3) + (b3 * b1 - b2 * b2)) / (b1 - b2);
        System.out.println(b4);
    }
}