import java.util.*

private val readString: ()->String = {readLine()!!}
private val readInt: ()->Int = { readLine()!!.toInt() }
private val readLong: ()->Long = { readLine()!!.toLong() }
private val readListInt: ()->List<Int> = { readLine()!!.split(' ').map(String::toInt) }
private val readListLong: ()->List<Long> = { readLine()!!.split(' ').map(String::toLong) }


fun main(args: Array<String>) {
    val (A, B,N) = readListLong()

    val x = if (N >= B-1) B-1 else N;

    val ans = A*x/B - A *(x/B)
    println(ans)
}
