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# (Mono-mcs 6.8.0.105) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Numerics;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp2
{
    class Program
    {
        static void Main(string[] args)
        {
            var ABN = Console.ReadLine().Split().Select(s => decimal.Parse(s)).ToArray();
            var A = ABN[0];
            var B = ABN[1];
            var N = ABN[2];
            decimal left = 0;
            decimal right = N;
            while(Math.Floor(left)< Math.Floor(right))
            {
                var lv = Math.Floor((A * left / B)) - A * Math.Floor(left / B);
                var rv = Math.Floor((A * right / B)) - A * Math.Floor(right / B);
                if(lv<rv)
                {
                    left += (right- left) / 2;
                    continue;
                }
                right -= (right - left) / 2;
            }
            var lvv = Math.Floor((A * left / B)) - A * Math.Floor(left / B);
            var rvv = Math.Floor((A * right / B)) - A * Math.Floor(right / B);
            Console.WriteLine(Math.Max(lvv, rvv));
        }
    }
}