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#include<bits/stdc++.h>
 
using namespace std;
 
using ll = long long;
using vi = vector<int>;
using pi = pair<int, int>;
using vpi = vector<pi>;
#define FOR(x, b, e) for(int x = b; x <= (e); ++x)
#define FORD(x, b, e) for(int x = b; x >= (e); --x)
#define REP(x, n) for(int x = 0; x < (n); ++x)
#define ALL(c) (c).begin(), (c).end()
#define ALLD(c) (c).rbegin(), (c).rend()
#define SIZE(x) ((int)(x).size())
#define pb push_back
#define pp emplace_back
#define st first
#define nd second
#define sq(a) (a)*(a)
const int inf = 1000000001;
const double eps = 1e-9;
bool fleq(double a, double b){
	return abs(a - b) < eps;
}

int n;
int dp(vector<int>a, int f){
	int ans = 0;
	for(int i = 1; i < n; i++){
		if((i+f)%2 == 1){
			if(a[i] >= a[i - 1]){
				ans++;
				a[i] = -inf;
			}
		}
		else{
			if(a[i] <= a[i - 1]){
				ans++;
				a[i] = inf;
			}
		}
	}
	return ans;
}
int main(){
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cin >> n;
	vi a(n);
	for(int &x : a)cin >> x;
	cout << min(dp(a, 0), dp(a, 1)) << '\n';
	return 0;
}