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#include<bits/stdc++.h>
using namespace std;
using LL=long long;
#define FOR(i,l,r) for(int i=(l);i<=(r);++i)
#define REP(i,n) FOR(i,0,(n)-1)
#define ssize(x) int(x.size())
template<class A,class B>auto&operator<<(ostream&o,pair<A,B>p){return o<<'('<<p.first<<", "<<p.second<<')';}
template<class T>auto operator<<(ostream&o,T x)->decltype(x.end(),o){o<<'{';int i=0;for(auto e:x)o<<(", ")+2*!i++<<e;return o<<'}';}
#ifdef DEBUG
#define debug(x...) cerr<<"["#x"]: ",[](auto...$){((cerr<<$<<"; "),...);}(x),cerr<<'\n'
#else
#define debug(...) {}
#endif

int main() {
	cin.tie(0)->sync_with_stdio(0);

    int n;
    cin >> n;
    vector<int> a(n);
    REP(i, n) cin >> a[i];
    debug(n, a);
    int ans = n;
    REP(kk, 2) {
        int cnt = 0;
        vector<bool> used(n);
        REP(i, n - 1) {
            if (used[i])
                continue;
            if ((i % 2 == 0 and a[i] <= a[i + 1]) or (i % 2 == 1 and a[i] >= a[i + 1])) {
                used[i + 1] = true;
                ++cnt;
            }
        }
        ans = min(ans, cnt);
        for (auto& e : a)
            e = -e;
    }
    cout << ans << '\n';
}