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: Wrong Answer)

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;

namespace Main
{
    class Program
    {
        static void Main(string[] args)
        {
            //ここから
            //string[] str = Console.ReadLine().Split(' ');
            //int n = int.Parse(Console.ReadLine());
            string[] str = Console.ReadLine().Split(' ');

            var a = long.Parse(str[0]);
            var b = long.Parse(str[1]);
            var n = long.Parse(str[2]);

            long mae = a * n / b;
            long usiro = n / b;

            long max = mae-a*usiro;

            if (b < n)
            {
                max = Max(max,a * (b - 1) / b);
                
            }

            /*for (long i = 1; i < n; i++)
            {
                mae = a * i / b;
                usiro = i / b;
                long temp = mae-a*usiro;
                Console.WriteLine("{0} notoki {1}", i, temp);
                max = Max(temp, max);
                if (i > b) break;
            }*/

            Console.WriteLine(max);

            //ここまで
        }

        static long Max(long a, long b)
        {
            if (a > b) return a;
            else return b;
        }


    }

}