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

for i in 0...A.count - 3{
    let numMax = A[i...i + 2].max()
    let numMid = A[i + 1]
    if numMid == numMax{
        if A[0] != A[2]{
            Kado += 1
        }
    }
}

print(Kado)