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// Author: Kajetan Ramsza
#include "bits/stdc++.h"

using namespace std;

template<typename F, typename S> ostream& operator<<(ostream& os, const pair<F, S> &p) { return os<<"("<<p.first<<", "<<p.second<<")"; }
template<typename T> ostream &operator<<(ostream & os, const vector<T> &v) { os << "{"; typename vector< T > :: const_iterator it;
    for( it = v.begin(); it != v.end(); it++ ) { if( it != v.begin() ) os << ", "; os << *it; } return os << "}"; }

void dbg_out() { cerr<<'\n'; }
template<typename Head, typename... Tail> void dbg_out(Head H, Tail... T) { cerr<<' '<<H; dbg_out(T...); }

#ifdef DEBUG
#define dbg(...) cerr<<"(" << #__VA_ARGS__ <<"):", dbg_out(__VA_ARGS__)
#else
#define dbg(...) 
#endif

typedef long long ll;

const int max_val = 1e9;

int n;

int solve(vector<int> vec, bool parity) {
	int res = 0;
	for(int i=1;i<n;i++) {
		if(i % 2 == parity) {
			if(vec[i] <= vec[i-1]) {
				vec[i] = max_val; 
				res++;
			}
		} else {
			if(vec[i] >= vec[i-1]) {
				vec[i] = -max_val; 
				res++;
			}
		}
	}
	return res;
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
	
	cin>>n;
	vector<int> vec(n);
	for(auto &v : vec)
		cin>>v;
	int res1 = solve(vec, 0);
	int res2 = solve(vec, 1);
	dbg(res1, res2);
	cout<<min(res1, res2)<<'\n';
}