using System;
using static System.Console;
using System.Text;
using System.Linq;
using static System.Math;
using System.Collections.Generic;
using System.Threading.Tasks;
using System.IO;
using System.Diagnostics;

class Program
{
    public static int count = 0;
    static void Main(string[] args)
    {
        var alg = new cp();
        //var n=inputInt();
        //var s=inputString();
        //var arr=inputSplitInt();
        //var jug=inputJaggedArrayInt(n);
        var abt = alg.inputSplitInt();
        var a = abt[0];//A秒 2A秒・・
        var b = abt[1];//ビスケット枚数
        var t = abt[2];//time
        int count = 0;
        double t2 = t+0.5;
        while (t2>0)
        {
            t2 -= (count + 1) * a-(count)*a;
            if (t2>=0)
            {
                count++;
            }
        }
        WriteLine(count*b);
    }
}

class cp
{

    public cp()
    {
    }
    public int GCD(int a, int b)
    {
        return a % b == 0 ? b : GCD(b, a % b);
    }
    public int LCM(int a, int b)
    {
        return a * b / GCD(a, b);
    }
    public int countChar(string s, string key)
    {
        return s.Length - s.Replace(key, "").Length;
    }
    public string YesNo(bool f, string type = null)
    {
        string str;
        if (f) str = "Yes"; else str = "No";
        if (type == "lower") return str.ToLower(); else if (type == "upper") return str.ToUpper(); else return str;
    }
    public void inputSkip()
    {
        ReadLine();
        return;
    }
    public string inputString()
    {
        return ReadLine();
    }
    public string[] inputSplitString()
    {
        return ReadLine().Split();
    }
    public string[] inputLinesString(int len)
    {
        var arr = new string[len];
        for (int a = 0; a < len; a++)
        {
            arr[a] = ReadLine();
        }
        return arr;
    }
    public string[][] inputJaggedArrayString(int len)
    {
        var arr = new string[len][];
        for (int a = 0; a < len; a++)
        {
            arr[a] = ReadLine().Split();
        }
        return arr;
    }
    public int inputInt()
    {
        return int.Parse(ReadLine());
    }
    public int[] inputSplitInt()
    {
        return ReadLine().Split().Select(i => int.Parse(i)).ToArray();
    }
    public int[] inputLinesInt(int len)
    {
        var arr = new int[len];
        for (int a = 0; a < len; a++)
        {
            arr[a] = int.Parse(ReadLine());
        }
        return arr;
    }
    public int[][] inputJaggedArrayInt(int len)
    {
        var arr = new int[len][];
        for (int a = 0; a < len; a++)
        {
            arr[a] = ReadLine().Split().Select(i => int.Parse(i)).ToArray();
        }
        return arr;
    }
    public long inputLong()
    {
        return long.Parse(ReadLine());
    }
    public long[] inputSplitLong()
    {
        return ReadLine().Split().Select(i => long.Parse(i)).ToArray();
    }
    public long[] inputLinesLong(int len)
    {
        var arr = new long[len];
        for (int a = 0; a < len; a++)
        {
            arr[a] = long.Parse(ReadLine());
        }
        return arr;
    }
    public long[][] inputJaggedArrayLong(int len)
    {
        var arr = new long[len][];
        for (int a = 0; a < len; a++)
        {
            arr[a] = ReadLine().Split().Select(i => long.Parse(i)).ToArray();
        }
        return arr;
    }
    public double inputDouble()
    {
        return double.Parse(ReadLine());
    }
    public double[] inputSplitDouble()
    {
        return ReadLine().Split().Select(i => double.Parse(i)).ToArray();
    }
    public double[] inputLinesDouble(int len)
    {
        var arr = new double[len];
        for (int a = 0; a < len; a++)
        {
            arr[a] = double.Parse(ReadLine());
        }
        return arr;
    }
    public double[][] inputJaggedArrayDouble(int len)
    {
        var arr = new double[len][];
        for (int a = 0; a < len; a++)
        {
            arr[a] = ReadLine().Split().Select(i => double.Parse(i)).ToArray();
        }
        return arr;
    }
}

Measured memory_bytes: 13396