Problem:
Score : 400 points

Problem Statement

Given are integers A, B, and N.

Find the maximum possible value of floor(Ax/B) - A × floor(x/B) for a non-negative integer x not greater than N.

Here floor(t) denotes the greatest integer not greater than the real number t.

Constraints

1 ≤ A ≤ 10^{6}

1 ≤ B ≤ 10^{12}

1 ≤ N ≤ 10^{12}

All values in input are integers.

Input

Input is given from Standard Input in the following format:

A B N

Output

Print the maximum possible value of floor(Ax/B) - A × floor(x/B) for a non-negative integer x not greater than N, as an integer.

Sample Input 1

5 7 4

Sample Output 1

2

When x=3, floor(Ax/B)-A×floor(x/B) = floor(15/7) - 5×floor(3/7) = 2. This is the maximum value possible.

Sample Input 2

11 10 9

Sample Output 2

9

Solution in C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
class Program
{
    static void Main(string[] args)
    {
            // 入力
            string[] sS = System.Console.ReadLine().Trim().Split(' ');
            decimal iA = decimal.Parse(sS[0]);
            decimal iB = decimal.Parse(sS[1]);
            decimal iN = decimal.Parse(sS[2]);

            System.Diagnostics.Stopwatch sw = new System.Diagnostics.Stopwatch();
            sw.Start();

            // 解析
            List<decimal> lstMin = new List<decimal>();
            lstMin.Add(iB - 1);
            lstMin.Add(iN);
            lstMin.Sort();
            decimal iMax = lstMin[0];
            decimal iOne = Math.Truncate(iA * iMax / iB) - iA * Math.Truncate(iMax / iB);
            //List<decimal> lstRet = new List<decimal>();
            //for (decimal i = 0; i <= iMax; i++)
            //{
            //    decimal iOne = Math.Truncate(iA * i / iB) - iA * Math.Truncate(i / iB);
            //    if (lstRet.Contains(iOne) && lstRet[lstRet.Count - 1] != iOne) { break; }
            //    lstRet.Add(iOne);
            //}
            //lstRet.Sort();
            //lstRet.Reverse();

            // 出力
            System.Console.WriteLine("{0}", iOne.ToString().Trim());

            sw.Stop();
#if DEBUG
            Console.WriteLine();
            Console.WriteLine("{0}", sw.Elapsed.ToString());
            Console.WriteLine("続行するには何かキーを押してください．．．");
            Console.ReadKey();
#endif
    }

}