using System.Collections.Generic; using System.Linq; using static System.Console; class Program { static void Main() { var hand = NextInt() * 60L; var runCost = NextInt(); var initCost = NextInt() * 3600L; if (hand <= runCost) { WriteLine(-1); return; } WriteLine((initCost - 1) / (hand - runCost) + 1); } static int NextInt() { return int.Parse(NextString()); } static string NextString() { var result = new List(); while (true) { int next = Read(); if (next < 0) break; var nextChar = (char)next; if (!char.IsWhiteSpace(nextChar)) result.Add(nextChar); else if (nextChar != '\r') break; } return string.Join("", result); } }