import java.util.*
import kotlin.math.floor
import kotlin.math.min


fun main() {
    val sc = Scanner(System.`in`)
    val a = sc.nextInt()
    val b = sc.nextLong()
    val n = sc.nextLong()

    val x = min(b-1, n)
    
    println((floor(a * x / b.toDouble()) - a * floor(x / b.toDouble())).toInt())

}

/*


floor(x * a / b) - a * floor(x / b) の最大値

 */
