class Program
    {
        static void Main(string[] args)
        {
            string[] tree = Console.ReadLine().Split(' ');
            int maxLeaf = int.Parse(tree[0]);
            int decrease = int.Parse(tree[1]);
            int month = int.Parse(tree[2]);
            int count = 0;
            List<int> list = new List<int>();
            for(int i = 0; i < int.Parse(tree[3]); i++)
            {
                list.Add(month);
                month++;
                if(month == 13)
                {
                    month = 1;
                }
            }
            month = 1;
            while(maxLeaf > 0)
            {
                count++;
                if( list.IndexOf(month) == -1)
                {
                    maxLeaf -= decrease;
                }
                else
                {
                    maxLeaf -= decrease * 2;
                }
                month++;
                if(month == 13) { month = 1; }
            }
            Console.WriteLine(count);
        }
    }