import java.io.*;
import java.util.*;


public class Main_yukicoder538 {

	private static Scanner sc;
	private static Printer pr;

	private static void solve() {
		long b1 = sc.nextInt();
		long b2 = sc.nextInt();
		long b3 = sc.nextInt();

		long r1 = b2 - b3;
		long r2 = b1 - b2;
		long d1 = b3 * b1 - b2 * b2;
//		long d2 = b2;

		long d4 = (r1 * b3 + d1) / r2;
		pr.println(d4);
	}

	// ---------------------------------------------------
	public static void main(String[] args) {
		sc = new Scanner(System.in);
		pr = new Printer(System.out);

		solve();

		pr.close();
		sc.close();
	}

	private static class Printer extends PrintWriter {
		Printer(PrintStream out) {
			super(out);
		}
	}
}