import java.util.*

fun main(args: Array<String>) {
    val scanner = Scanner(System.`in`)
    val a = scanner.nextLong()
    val b = scanner.nextLong()
    val n = scanner.nextLong()
    if(b>n){
        println(a*n/b)
    }
    else if(b===n){
        println(a*(n-1)/b)
    }
    else{
        println(Math.max((a*n/b)-(n/b*a), (a*(b-1)/b)))
        //println((Math.floor((a*n/b.toDouble())).toLong())-(a*Math.floor((n/b.toDouble())).toLong()))
    }
}