[CCF CSP] 201604-1 break point count

Problem description

　　 Given n An integer represents a store in succession n Days of sales . If sales were up one day , The next day sales are down , Call this day a discount point , In turn, if the previous sales decrease and the sales increase the next day , Also called this day a discount point . Other days are not discount points . As shown in the figure below , The first 3 Day and day 6 It's a discount .

　　 Given n It's an integer a1, a2, …, an Sales volume , Please work out how many discount points there are in total these days .
　　 To reduce ambiguity , The data we give guarantee ： Here n The sales volume of the next two days is always different , namely ai-1≠ai. Be careful , If two days are not adjacent , Sales may be the same .

Input format

　　 The first line of input contains an integer n.
　　 The second line contains n It's an integer , Separate... With spaces , respectively a1, a2, …, an.

Output format

　　 Output an integer , Indicates the number of fold points .

The sample input

7
5 4 1 2 3 6 4

Sample output

2

Evaluate use case size and conventions

　　 All evaluation cases meet ：1 ≤ n ≤ 1000, The sales volume is no more than 10000 Non-negative integer .