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

val sc = Scanner(System.`in`)

fun main(args: Array<String>) {

    val A = sc.nextLong().toDouble()
    val B = sc.nextLong().toDouble()
    val N = sc.nextLong().toDouble()

    val x = if(N < B - 1) N else B - 1
    val ans = floor(A * x / B) - A * floor(x / B)
    println(ans.toInt())
}

