import java.util.*;

public class Main {
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	long a = sc.nextInt();
    	long b = sc.nextInt();
    	long c = sc.nextInt();
    	double d = (b * b - a * c) / (b - a);
    	double r = (b - d) / a;
    	long ans = (long)(c * r + d);
    	System.out.println(ans);
    }
}