using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;

namespace No1
{
    class Program
    {
        static void Main(string[] args)
        {
            int l, n, v, t;
            String[] s1;
            using (StreamReader r = new StreamReader("input.txt"))
            {
                s1 = r.ReadLine().Split(' ');
                l = int.Parse(s1[0]);
                n = int.Parse(s1[1]);
                v = int.Parse(s1[2]);
                t = int.Parse(s1[3]);
            }

            int length = l / n;
            int cur_length = v * t;

            while (cur_length > l)
            {
                cur_length -= l;
            }

            int count = cur_length / length + 1;

            if (count > l)
            {
                count = l - count;
            }

            using (StreamWriter w = new StreamWriter("output.txt"))
            {
                w.WriteLine(Math.Abs(count));
            }
        }
    }
}