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#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")

#include <bits/stdc++.h>

using namespace std;

void solve() {
    int n;
    cin >> n;
    vector<int> v(n);
    for (int i = 0; i < n; i++) {
        cin >> v[i];
    }
    int res1 = 0, res2 = 0;
    bool real = false;
    for (int i = 0; i < n; i++) {
        if (i & 1) {
            if (real && v[i - 1] >= v[i]) {
                res1++;
                real = false;
            } else {
                real = true;
            }
        } else {
            if (real && v[i - 1] <= v[i]) {
                res1++;
                real = false;
            } else {
                real = true;
            }
        }
    }
    real = false;
    for (int i = 0; i < n; i++) {
        if (i & 1) {
            if (real && v[i - 1] <= v[i]) {
                res2++;
                real = false;
            } else {
                real = true;
            }
        } else {
            if (real && v[i - 1] >= v[i]) {
                res2++;
                real = false;
            } else {
                real = true;
            }
        }
    }
    cout << min(res1, res2) << endl;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(0);

// #ifdef LOCAL
//     int t; cin >> t; while (t--)
// #endif

    solve();

    cout.flush();
}