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#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int minHeightChanges(const vector<int>& h, bool firstIsHigh) {
    int cnt = 0;
    int result = 0;
    bool prevShouldBeHigher = firstIsHigh;

    for (int i = 1; i < h.size(); ++i) {
        if ((prevShouldBeHigher && h[i - 1] <= h[i]) || (!prevShouldBeHigher && h[i - 1] >= h[i])) {
            cnt++;
        } else if (cnt > 0) {
            result += (cnt + 1) / 2;
            cnt = 0;
        }
        prevShouldBeHigher = !prevShouldBeHigher;
    }
    if (cnt > 0) {
        result += (cnt + 1) / 2;
    }
    return result;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int n, x;
    vector<int> h;
    cin >> n;
    for (int i = 0; i < n; ++i) {
        cin >> x;
        h.emplace_back(x);
    }

    cout << min(minHeightChanges(h, false), minHeightChanges(h, true));

    return 0;
}