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#include <iostream>

using namespace std;

int main() {

    ios_base::sync_with_stdio(0);
    cin.tie(0);

    int MAX = 1000000;
    int MIN = -1000000;
    int MAX_N = 50001;

    int n;
    int t[MAX_N];
    cin >> n;
    for(int i=0; i<n; i++) {
        cin >> t[i];
    }

    int best_a, best_b;
    {
        int tmp[MAX_N];
        for (int i = 0; i < n; i++) {
            tmp[i] = t[i];
        }

        int start = 0;
        // zaczynamy od dolu
        for (int i = 0; i < n; i += 2) {
            if (tmp[i] == MAX) {
                tmp[i] = MIN;
                start++;
            }
        }
        for (int i = 1; i < n; i += 2) {
            if (tmp[i] == MIN) {
                tmp[i] = MAX;
                start++;
            }
        }

        int best[MAX_N][2];
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < 2; j++) {
                best[i][j] = 0;
            }
        }


        int idx;
        if (n % 2 == 0) {
            idx = n - 2;
            tmp[n] = MIN;
            best[n][false] = best[n][true] = 0;
        } else {
            idx = n - 3;
            best[n - 1][true] = 0;
            best[n - 1][false] = 1;
        }

        for (; idx >= 0; idx -= 2) {
            bool current_ok = tmp[idx] < tmp[idx + 1];
            bool future_ok = tmp[idx + 1] > tmp[idx + 2];

//        if(current_ok) {
            best[idx][true] = min(!current_ok + best[idx + 2][future_ok], 1 + best[idx + 2][true]);
            best[idx][false] = min(1 + best[idx + 2][future_ok], 2 + best[idx + 2][true]);
//        } else {
//            best[idx][true] = min(1 + best[idx+2][future_ok], 1 + best[idx+2][true]);
//            best[idx][false] = min(1 + best[idx+2][future_ok], 1 + best[idx+2][true]);
//        }

//        cout << idx << ": " << best[idx][true] << " " << best[idx][false] << endl;

        }

        best_a = start + best[0][true];
    }


    {
        int tmp[MAX_N];
        for(int i=0; i<n; i++) {
            tmp[i] = t[i];
        }

        int start = 0;
        // gora
        for(int i=0; i<n; i+=2) {
            if(tmp[i] == MIN) {
                tmp[i] = MAX;
                start++;
            }
        }
        for(int i=1; i<n; i+=2) {
            if(tmp[i] == MAX) {
                tmp[i] = MIN;
                start++;
            }
        }

        int best[MAX_N][2];
        for(int i=0; i<n; i++) {
            for(int j=0; j<2; j++) {
                best[i][j] = 0;
            }
        }



        int idx;
        if(n % 2 == 0) {
            idx = n-2;
            tmp[n] = MAX+1;
            best[n][false] = best[n][true] = 0;
        } else {
            idx = n-3;
            best[n-1][true] = 0;
            best[n-1][false] = 1;
        }

        for(; idx >= 0; idx -= 2) {
            bool current_ok = tmp[idx] > tmp[idx+1];
            bool future_ok = tmp[idx+1] < tmp[idx+2];

//        if(current_ok) {
            best[idx][true] = min(!current_ok + best[idx+2][future_ok], 1 + best[idx+2][true]);
            best[idx][false] = min(1 + best[idx+2][future_ok], 2 + best[idx+2][true]);
//        } else {
//            best[idx][true] = min(1 + best[idx+2][future_ok], 1 + best[idx+2][true]);
//            best[idx][false] = min(1 + best[idx+2][future_ok], 1 + best[idx+2][true]);
//        }

//        cout << idx << ": " << best[idx][true] << " " << best[idx][false] << endl;

        }

        best_b = start + best[0][true];

        int res = min(best_a, best_b);

        cout << res << endl;

    }















}