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#include <bits/stdc++.h>
using namespace std;
 
using ll = long long;
using db = double;
using ull = unsigned long long;
 
using pi = pair<int, int>;
using pl = pair<ll, ll>;
 
using vi = vector<int>;
using vl = vector<ll>;
using vpi = vector<pi>;
using vpl = vector<pl>;
 
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define f first
#define s second
 
#define tcT template<class T
#define tcTU tcT, class U
 
#define sz(x) int((x).size())
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define rep(i,a,b) for(int i = (a); i < (b); i++)
#define rrep(i,a,b) for(int i = (b) - 1; i >= (a); i--)
 
const db PI = acos(-1);
mt19937 rng((uint32_t)chrono::steady_clock::now().time_since_epoch().count());
 
tcT> bool ckmin(T& a, const T& b) { return b < a ? a=b, 1 : 0; }
tcT> bool ckmax(T& a, const T& b) { return a < b ? a=b, 1 : 0; }
 
tcT> void _dbg(const char *sdbg, T h){ cerr<<sdbg<<'='<<h<<endl; }
tcT, class... TA> void _dbg(const char *sdbg, T h, TA... a) {
	while(*sdbg!=',') cerr<<*sdbg++;
	cerr<<'='<<h<<','; _dbg(sdbg+1, a...);
}
 
tcT> ostream &operator<<(ostream& os, vector<T> V) {
	os << "["; for (auto vv : V) os << vv << ","; return os << "]";
}
tcT, class V> ostream &operator<<(ostream &os, pair<T,V> P) {
	return os << "(" << P.f << "," << P.s << ")";
}
 
#ifdef LOCAL
#define debug(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#else
#define debug(...) (__VA_ARGS__)
#define cerr if(0)cout
#endif

int n;
const int INF = 1e9;
int finalres = INF;

void solve(vi a) {
	int res = 0;
	rep(i,1,n) {
		if (i%2 == 1 && a[i] >= a[i-1]) {
			a[i] = -INF;
			res++;
		}
		else if (i%2 == 0 && a[i] <= a[i-1]) {
			a[i] = INF;
			res++;
		}
	}
	ckmin(finalres, res);
}

signed main() {
	ios_base::sync_with_stdio(false); cin.tie(nullptr);

	cin >> n;
	vi a(n);
	rep(i,0,n) cin >> a[i];
	solve(a);
	rep(i,0,n) a[i] = -a[i];
	solve(a);

	cout << finalres << "\n";

	return 0;
}