//{{{
#include <bits/stdc++.h>
using namespace std;
#define rep(...) repN((__VA_ARGS__,rep3,rep2,loop,~))(__VA_ARGS__)
#define loop(n) rep2(_loop_,n)
#define rep2(i,n) rep3(i,0,n)
#define rep3(i,begin,end) for(int i=(int)(begin),i##_end=(int)(end);i<i##_end;++i)
#define repN(a) repX a
#define repX(a0,a1,a2,x,...) x
typedef long long ll;
const int MOD = 1e9+7;
//}}}

int a[100];
int main(){
	int N;
	cin >> N;
	rep(i, N) cin >> a[i];
	int ans = 0;
	rep(i, N - 2){
		ans += (a[i] < a[i + 1] && a[i + 1] > a[i + 2] && a[i] != a[i + 2]);
		ans += (a[i] > a[i + 1] && a[i + 1] < a[i + 2] && a[i] != a[i + 2]);
	}
	cout << ans << endl;
	return 0;
}