Six identical cards are placed on a table. Each card has the number $\text{'}1\text{'}$marked on one side and the number $\text{'}2\text{'}$marked on its other side. All the six cards are placed in such a manner that the number $\text{'}1\text{'}$ is on the upper side. In one try, exactly four (neither more nor less) cards are turned upside down. In how many least number of tries can the cards be turned upside down such that all the sic cards show the number $\text{'}2\text{'}$ on the upper side?