using System.Numerics;

public class Program
{
    public static void Main()
    {

        //BigInteger num = BigInteger.Parse(Console.ReadLine() ?? string.Empty);
        //int num = int.Parse(Console.ReadLine() ?? string.Empty);
        string[] moji = (Console.ReadLine() ?? string.Empty).Trim().Split(' ');
        //string str = Console.ReadLine() ?? string.Empty;



        var t = Console.ReadLine()!.Split();
        BigInteger A = BigInteger.Parse(t[0]);
        BigInteger B = BigInteger.Parse(t[1]);
        BigInteger C = BigInteger.Parse(t[2]);

        if (A == C)
        {
            Console.WriteLine(1);
            return;
        }

        if (A < C)
        {
            Console.WriteLine(-1);
            return;
        }

        BigInteger n = B / (A - C) + 1;
        Console.WriteLine(n);


    }
}