import scala.io.StdIn.readLine
import scala.io.StdIn.readInt

object Main extends App {
    val abn = readLine.split(" ").map(_.toLong)
    val a = abn(0)
    val b = abn(1)
    val n = abn(2)
    def f(a:Long,b:Long,x:Long): Long = {
        (a*x/b)-a*(x/b)
    }
    if(n>=b-1) print(f(a,b,b-1));
    else print(f(a,b,n));
}