#include <algorithm>
#include <bitset>
#include <cctype>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#define FOR(x,a,b) for(int x=a;x<b;x++)
#define FORSIZE(x,A) for(int x=0;x<A.size();x++)
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define SORT(x) sort(x.begin(),x.end())
#define RSORT(x) sort(x.rbegin(),x.rend())
#define rsort(x,n) sort(x, x+n, greater<int>())
#define REV(x) reverse(x.begin(),x.end())
#define REP(x,a) FOR(x,0,a)
using namespace std;
typedef long long ll;
inline int toInt(std::string s) {int v; std::istringstream sin(s);sin>>v;return v;}
template<class T> inline std::string toString(T x) {std::ostringstream sout;sout<<x;return sout.str();}

int main( int argc, const char* argv[] )
{
    int N;
    int A[200];
    int res;
    cin >> N;
    REP(i,N) cin >> A[i];

    FOR(i,0,N-2) {
        if(A[i] != A[i+1] && A[i] != A[i+2] && A[i+1] != A[i+2]) {
            if(!(A[i] < A[i+1] && A[i+1] < A[i+2]) && !(A[i] > A[i+1] && A[i+1] > A[i+2])) {
                res += 1;
            }
        }
    }
    cout << res << endl;
    return 0;
}