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 Kotlin (1.3.71) (judge verdict: Time Limit Exceeded)

import java.util.*

fun main(args: Array<String>) {
  val sc = Scanner(System.`in`)
  val a = sc.nextInt()
  val b = sc.nextLong()
  val n = sc.nextLong()

  println(abc165d(a, b, n))
}

private fun abc165d(a: Int, b: Long, n: Long): Int {
  val ansList = mutableListOf<Double>()
  ansList.add(0.0)
  var minCount = 0
  var before = 0.0
  for (i in 1..n) {
    val first = Math.floor(((a * i)/b).toDouble())
    if (first == 0.0) continue
    val tmp = first - 5 * Math.floor((i/b).toDouble())
    if (tmp < before) {
      minCount++
      if (minCount > 2) break;
    }

    ansList.add(tmp)
    before = tmp
  }
  val ans = ansList.max()!!
  return ans.toInt()
}