def dif(a,b,c):
    return (a!=b and b!=c and c!=a)

def main():
    n=int(input())
    l_list=list(map(int,input().split()))
    cnt=0
    for i in range(len(l_list)-2):
        a=l_list[i]
        b=l_list[i+1]
        c=l_list[i+2]
        cnt=cnt+1 if dif(a,b,c) and (b==max(a,b,c) or b==min(a,b,c)) else cnt
    print(cnt)
        
        


if __name__ == "__main__":
    main()