import kotlin.math.*
import java.util.*

fun main(args: Array<String>) {
  val (a, b, n) = readLine()!!.split(' ').map(String::toLong)
  val x = min(b - 1, n)
  val y = floor(a * x / b.toDouble()).toLong() - a * floor(x / b.toDouble()).toLong()
  println(y)
}
