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// clang-format off
#include <bits/stdc++.h>

using namespace std;

#define ALL(x) (x).begin(), (x).end()

template<class C> void mini(C &a5, C b5) { a5 = min(a5, b5); }
template<class C> void maxi(C &a5, C b5) { a5 = max(a5, b5); }

#ifdef LOCAL
const bool debug = true;
#else
const bool debug = false;
#define cerr if (true) {} else cout
#endif
// clang-format on

// #define int long long
#define double long double

const int INF = 1e9;
const int mod = 1e9 + 7;

int solve(vector<int> v) {
	int res = 0;
	for (int i = 0; i+1 < (int)v.size(); i++) {
		if (i % 2 == 0) { // i: P
			if (v[i] >= v[i+1]) {
				v[i+1] = INF;
				res++;
			}
		} else { // i: N
			if (v[i] <= v[i+1]) {
				v[i+1] = -INF;
				res++;
			}
		}
	}
	return res;
}

int32_t main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

	vector<int> v;
    int n;
    cin >> n;

    for (int i = 0; i < n; i++) {
		int a;
		cin >> a;
		v.push_back(a);
	}
	
	int res = solve(v);
	v.insert(v.begin(), -INF);
	int res2 = solve(v);
	
	cerr << res << " " << res2 << endl;
	cout << min(res, res2) << "\n";

    return 0;
}/*
5
4 1 3 3 1
* 
4
-1000000 -1000000 -1000000 -1000000
*/