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: Time Limit Exceeded)

using System;

namespace AtCoder
{
    public static class AtCoder
    {
        public static void Main()
        {
            var input = Console.ReadLine().Split(' ');
            long a = long.Parse(input[0]);
            long b = long.Parse(input[1]);
            long n = long.Parse(input[2]);

            long ans = -1;
            for (long i = n; i * a >= b; i--)
            {
                long check = (long)Math.Floor((double)(a * i / b)) - a * (long)Math.Floor((double)(i / b));
                ans = Math.Max(ans, check);
            }

            Console.WriteLine(ans);
        }
    }
}