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#include <bits/stdc++.h>
 
using namespace std;
 
#define endl '\n'
#define L long long
#define MP make_pair
#define REP(i, n) for(int i = 0; i < n; ++i)
#define REPR(i, n) for(int i = n - 1; i >= 0; --i)
#define FOR(i, a, b) for(int i = a; i < b; ++i)
#define FORR(i, a, b) for(int i = b - 1; i >= a; --i)
#define EB emplace_back
#define ST first
#define ND second
#define S size
#define RS resize
 
template<class T> using P = pair<T, T>;
template<class T> using V = vector<T>;

int n;

int solve(V<int> a, int s) {
    int swaps = 0;

    FOR(i, 1, n) {
        int sign = (i + s) % 2 == 0 ? 1 : -1;
        if (sign * (a[i] - a[i - 1]) <= 0) {
            a[i] = sign * (int)1e9;
            swaps++;
        }
    }

    return swaps;
}
 
int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
 
    cin >> n;
    V<int> a(n);
    REP(i, n) {
        cin >> a[i];
    }

    cout << min(solve(a, 0), solve(a, 1)) << '\n';
}

// g++ -std=c++17 -Wall -Wextra -Wshadow -Wconversion -D_GLIBCXX_DEBUG orn.cpp -o orn