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.Collections.Generic;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        var inputs = Console.ReadLine().Split(' ').Select(long.Parse).ToArray();
        var a = inputs[0];
        var b = inputs[1];
        var n = inputs[2];

        var target = n / 2;
        long dis = 10000000;
        long ans = 0;

        for (long i = target - dis; i < target + dis; i++)
        {
            if (i < 0) continue;
            if (i > n) continue;

            var tmp = Math.Floor(((double)a / b) * i) - Math.Floor((double)i / b);
        
            long aaa = (long)tmp;
            if (aaa > ans) ans = aaa;
            
        }

        for(long i = 0; i < dis; i++)
        {
            if (i < 0) continue;
            if (i > n) continue;

            var tmp = Math.Floor(((double)a / b) * i) - Math.Floor((double)i / b);

            long aaa = (long)tmp;
            if (aaa > ans) ans = aaa;
        }

        for(long i = n; i > n - dis; i--)
        {
            if (i < 0) continue;
            if (i > n) continue;

            var tmp = Math.Floor(((double)a / b) * i) - Math.Floor((double)i / b);

            long aaa = (long)tmp;
            if (aaa > ans) ans = aaa;
        }

        for (long i = n * 2 / 3; i < n * 2 / 3 + dis; i++)
        {
            if (i < 0) continue;
            if (i > n) continue;

            var tmp = Math.Floor(((double)a / b) * i) - Math.Floor((double)i / b);

            long aaa = (long)tmp;
            if (aaa > ans) ans = aaa;
        }

        Console.WriteLine(ans);
    }

}