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;

public class MainClass
{
	public const long Giri = 1000000007;
	public const long DpInf = 99999999999999;
	
	public static void Main(string[] args)
	{
		var p = Input();
		var a = p[0].ToInt();
		var b = p[1].ToLong();
		var n = p[2].ToLong();
		
		long x = 0;
		if(n < b)
		{
			//Console.WriteLine(n-1);
			x = n;
		}
		else
		{
			//Console.WriteLine(n-1);
			x = b-1;
		}
		long k = (long)(Math.Floor((double)a * x / b) - a * Math.Floor((double)x/b));
		Console.WriteLine(k);
		/*
		long max = 0;
		for(long x = (b-1)/2; x <= Math.Min(n, b); x++)
		{
			long k = (long)(Math.Floor((double)a * x / b) - a * Math.Floor((double)x/b));
			//Console.WriteLine(k);
			max = Math.Max(max, k);
		}
		Console.WriteLine(max);
		*/
	}
	
	
	static long GCD(long a, long b)
	{
		var v = new[] { a, b };
		while (v[1] != 0) { v = new[] { v[1], v[0] % v[1] }; }
		return v[0];
	}
	public static string[] Input() { return Console.ReadLine().Split(); }
}

public static class Smarter
{
	public static int ToInt(this string str) { return int.Parse(str); }
	public static long ToLong(this string str) { return long.Parse(str); }
	public static int[] ToInt(this string[] str, int offset = 0)
	{
		var r = new int[str.Length];
		for(int i = 0; i < str.Length; i++) r[i] = str[i].ToInt() + offset;
		return r;
	}
}