Flip the cards

There are $N$ cards on a table, out of which $X$ cards are face-up and the remaining are face-down. In one operation, we can do the following: - Select any one card and flip it (i.e. if it was initially face-up, after the operation, it will be face-down and vice versa) What is the minimum number of operations we must perform so that all the cards face in the same direction (i.e. either all are