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

fun main(args: Array<String>) {
    val scan = Scanner(System.`in`)
    var (a,b,n) = scan.nextLine().split(" ").map{ it.trim().toLong() }.toTypedArray()

    var ans : Long= 0
    if(n<b)
        ans= ((a*n)/b)
    else if(n==b)
        ans = ((a*(n-1))/b)
    else
    {
        var x = (b-1)
        var k1 = ((a*x)/b)
        var k2 = (a*(x/b))
        ans=k1-k2
    }
    println(ans)
}
