import java.util.Scanner

case class Output(v: Int) {
  def print() {
    println(v)
  }
}

case class Input(a: Int, b: Int, c: Int) {
  private def enough(d: Int): Boolean = a * d + (d / 7) * b >= c
  private def binsearch {

  }
  def solve(): Output = {
    var lb = 0
    var ub = 1000000
    while (ub-lb > 1) {
      val m = (lb+ub)/2
      if (enough(m)) ub = m
      else lb = m
    }
    Output(ub)
  }
}

object Input {
  def read(): Input = {
    val scanner = new Scanner(System.in)
    Input(scanner.nextInt(), scanner.nextInt(), scanner.nextInt())
  }
}

object Main extends App {
  Input.read().solve().print()
}

