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.Text;

namespace CSharpTest
{
    class D_Floor
    {
        static void Main(string[] args)
        {
            string[] ABN = Console.ReadLine().Split();
            Int64 A = Int64.Parse(ABN[0]);
            Int64 B = Int64.Parse(ABN[1]);
            Int64 N = Int64.Parse(ABN[2]);
            if(N < B)
            {
                double Core = (double)N / (double)B;
                double Fraction = Core - Math.Floor(Core);
                Console.WriteLine(Math.Floor(Fraction * A));
            }
            else
            {
                double Core = (double)(B - 1) / (double)B;
                double Fraction = Core - Math.Floor(Core);
                Console.WriteLine(Math.Floor(Fraction * A));
            }
        }
    }
}