package Yukicoder

/**
 * Created by hichikawa on 2015/11/11.
 */
fun main(args: Array<String>) {
    fun readLineLong() : Long {
        val str = readLine() as String
        return str.toLong()
    }

    val inputLong = readLineLong() * 7
    if (inputLong % 2.toLong() == 0.toLong()) {
        println(inputLong / 2)
    } else {
        println(inputLong / 2.0)
    }
}