import kotlin.math.floor
import kotlin.math.sqrt

fun main() = abc165d()

@OptIn(ExperimentalStdlibApi::class)
fun abc165d() {
    val (a, b, n) = readLine()!!.split(' ').map { it.toLong() }

    val answer = floor(a.toDouble() * Math.min(b - 1, n) / b).toLong()

    println(answer)
}
