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#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,b) for (int i = (a); i <= (b); ++i)
#define REPD(i,a,b) for (int i = (a); i >= (b); --i)
#define FORI(i,n) REP(i,1,n)
#define FOR(i,n) REP(i,0,int(n)-1)
#define mp make_pair
#define pb push_back
#define pii pair<int,int>
#define vi vector<int>
#define ll long long
#define SZ(x) int((x).size())
#define DBG(v) cerr << #v << " = " << (v) << endl;
#define FOREACH(i,t) for (typeof(t.begin()) i=t.begin(); i!=t.end(); i++)
#define fi first
#define se second

int a[100100];

int main() {
	int n;
	scanf("%d", &n);
	FOR(i,n) scanf("%d", &a[i]);
	int it = 1, ans0 = 0, ans1 = 0;
	while (it < n) {
		if (it%2==0 && a[it]>a[it-1]) it++;
		else if (it%2==1 && a[it]<a[it-1]) it++;
		else {
			ans0++;
			it += 2;
		}
	}
	it = 1;
	while (it < n) {
		if (it%2==1 && a[it]>a[it-1]) it++;
		else if (it%2==0 && a[it]<a[it-1]) it++;
		else {
			ans1++;
			it += 2;
		}
	}
	printf("%d\n", min(ans0, ans1));
	return 0;
}