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 inp = Console.ReadLine().Split(' ');
        int A = int.Parse(inp[0]);
        long B = long.Parse(inp[1]);
        long N = long.Parse(inp[2]);

        long ans = -1;
        long tmp = -1;
        /*for(int i = 1;i < N + 1;i++) {
            Console.WriteLine((long)(A * i / B));
            Console.WriteLine(A * i / B);

            tmp = (long)(A * i / B) - A * (long)(i / B);
            if(tmp > ans) {
                ans = tmp;
            }
        }*/

        ans = (long)(A * N / B) - A * (long)(N / B);

        long index = B;
        long ib = index / B;
        while(true) {
            if(index >= N) break;

            tmp = (long)(A * index / B) - A * ib;
            if(tmp > ans) {
                ans = tmp;
            }

            index += B;
        }

        Console.WriteLine(ans);
    }
}