fun main(args: Array<String>) = ABC165D.main()

object ABC165D {
    fun log(message: Any?) {
        println(message)// TODO: ←消す
    }

    val A: Int
    val B: Long
    val N: Long

    init {
        val (a, b, n) = readLongs()
        A = a.toInt()
        B = b
        N = n
    }

    fun main() {
        //val ans = (1..N).map { x ->
        //    A * x / B - A * floorDiv(x,B)
        //}.max()

        if (B == 1L) {
            val ans = 0
            println(ans)
            return
        }

        val scores = (0..N / B - 1).asSequence().map { floor ->
            val x = (floor + 1) * B - 1
            A * x / B - A * floor
        } + sequenceOf(A * N / B - A * (N / B))

        val ans = scores.max()

        println(ans)
    }

    /*####################################################################################*/

    fun readLongs() = readLine()!!.split(" ").map { it.toLong() }
}