Bessie and her friend Elsie are currently playing a simple card game where they take a deck of 2N2N cards, conveniently numbered 1…2N1…2N, and divide them into NN cards for Bessie and NN cards for Elsie. The two then play NN rounds, where in each round Bessie and Elsie both play a single card, and the player with the highest card earns a point.
Given that Bessie can predict the order in which Elsie will play her cards, please determine the maximum number of points Bessie can win.
The first line of input contains the value of N (1≤N≤50,0001≤N≤50,000).
The next N lines contain the cards that Elsie will play in each of the successive rounds of the game. Note that it is easy to determine Bessie's cards from this information.
Output a single line giving the maximum number of points Bessie can score.