class TendonWalk:
    def __init__(self, destination: int):
        self.destination = destination
        self._init()

    def _init(self):
        self.point = 0
        self.distance = 0

    def move_a(self):
        self.point += 2
        self.distance += 2

    def move_b(self):
        self.point -= 1
        self.distance += 1

    def check_dest(self) -> bool:
        return self.point == self.destination

    def move(self) -> int:
        for _ in range(100):
            self.move_a()
            if self.check_dest():
                return
            self.move_a()
            if self.check_dest():
                return
            self.move_b()
            if self.check_dest():
                return
            self.move_b()
            if self.check_dest():
                return
            self.move_a()
            if self.check_dest():
                return
            self.move_b()
            if self.check_dest():
                return
            self.move_b()
            if self.check_dest():
                return


def main():
    X = int(input())
    simulator = TendonWalk(X)
    simulator.move()
    print(simulator.distance)


if __name__ == "__main__":
    main()