let N = Int(readLine()!)
let A = readLine()!.split(separator: " ").map{Int($0)!}
var kado = 0

for i in 0...A.count - 3{
    let nums: Set = Set(A[i...i + 2])
    let numCnt = nums.count
    let numMax = A[i...i + 2].max()
    let numMin = A[i...i + 2].min()
    let numMid = A[i + 1]
    if numMid == numMax || numMid == numMin{
        if numCnt == 3{
            kado += 1
        }
    }
}

print(kado)