#include <bits/stdc++.h>

typedef long long ll;
typedef unsigned long long ull;

#define FOR(i,a,b) for(int (i)=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define RANGE(vec) (vec).begin(),(vec).end()

using namespace std;


class PineDecorationSequence1 {
public:
    bool check(int a, int b, int c) {
            if (a == b || b == c || c == a)
                return false;
            vector<pair<int,int>> seq = {{a,0},{b,1},{c,2}};
            sort(RANGE(seq));
            return (seq[1].second == 0 || seq[1].second == 2);
    }
    void solve(void) {
            int N;
            cin>>N;

            vector<int> A(N);
            REP(i,N)
                cin>>A[i];

            deque<int> deq;
            int cnt = 0;
            REP(i,N)
            {
                if (deq.size() >= 3)
                    deq.pop_front();
                deq.push_back(A[i]);
                if (deq.size() < 3)
                    continue;
                if ( check(deq[0], deq[1], deq[2]))
                    ++cnt;
            }
            cout<<cnt<<endl;
    }
};

#if 1
int main(int argc, char *argv[])
{
        ios::sync_with_stdio(false);
        auto obj = new PineDecorationSequence1();
        obj->solve();
        delete obj;
        return 0;
}
#endif