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.io.PrintWriter
import kotlin.math.max

fun main() {
    val pw = PrintWriter(System.out)

    val (a, b, n) = readInputLine().split(" ").map { it.toLong() }

    var ans = 0L

    for (i in LongRange(n / 1000000L, n)) {
        ans = max(ans, a * i / b - a * (i / b))
    }

    pw.println(ans)

    pw.flush()
}

fun readInputLine(): String {
    return readLine()!!
}