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#include <bits/stdc++.h>

using namespace std;
#define endl '\n'
#define fi first
#define sc second
#define LL long long

int main(){
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	
	int N;
	cin >> N;
	vector<int> Tab(N);
	for(auto &x : Tab) cin >> x;
	int Result = 0;
	bool prevmin = false, prevmax = false, nmin = false, nmax = false;
	for(int i = 1; i < N; i++){ // zaczynamy do gory
		if(i % 2 == 1){
			if(!prevmin && !prevmax && Tab[i] <= Tab[i-1]){
				Result++;
				nmax = true;
			}		
		}
		else{
			if(!prevmin && !prevmax && Tab[i] >= Tab[i-1]){
				Result++;
				nmin = true;
			}
		}
		prevmax = nmax; nmax = false;
		prevmin = nmin; nmin = false;
	}
	prevmax = false; prevmin = false;
	int tempres = 0;
	for(int i = 1; i < N; i++){ // zaczynamy do gory
		if(i % 2 == 1){
			if(!prevmin && !prevmax && Tab[i] >= Tab[i-1]){
				tempres++;
				nmin = true;
			}		
		}
		else{
			if(!prevmin && !prevmax && Tab[i] <= Tab[i-1]){
				tempres++;
				nmax = true;
			}
		}
		prevmax = nmax; nmax = false;
		prevmin = nmin; nmin = false;
	}
	Result = min(Result, tempres);
	cout << Result << endl;
	return 0;
}