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#include <iostream>
#include <vector>

using namespace std;

const int mini = -10000000;
const int maxi = 10000000;

int continue_assuming_0_1(vector<int>& v) {
    int n = v.size();
    int res = 0; 
    for(int i = 2; i < n; i++) {
        bool malec = v[i-1] > v[i-2];
        if(malec) {
            if(v[i] < v[i-1]) {
                // ok
            } else {
                v[i] = mini;
                res++;
            }
        } else {
            if(v[i] > v[i-1]) {
                // ok
            } else {
                v[i] = maxi;
                res++;
            }
        }
    }
    return res;
}

int main()
{
    int n;
    cin >> n;
    
    vector<int> v(n);
    for(int i = 0; i < n; i++) 
        cin >> v[i];

    int best = 20000000;
    
    if(v[0] != v[1]) {
        // pierwsze 2 zostaja
        vector<int> v1 = v;
        int res = continue_assuming_0_1(v1);
        if(res < best) best = res;
    }
    
    vector<int> v1 = v;
    v1[1] = mini;
    int res = continue_assuming_0_1(v1) + 1;
    if(res < best) best = res;
    
    v1 = v;
    v1[1] = maxi;
    res = continue_assuming_0_1(v1) + 1;
    if(res < best) best = res;
    
    cout << best << endl;
    
    return 0;
}