import java.util.*

fun main() {
    q1712()
}

fun q1712() = with(Scanner(System.`in`)) {
    val a = nextDouble()
    val b = nextDouble()
    val c = nextDouble()

    if(b >= c) {
        println(-1);
        return
    }

    val result = a / (c - b)
    val resultCell = kotlin.math.ceil(result)
    if(result == resultCell) println((result.toInt() + 1)) else println(resultCell.toInt())
}