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//Franciszek Witt
#include<bits/stdc++.h>
using namespace std;
#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
typedef long long ll;
int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n;
    cin >> n;
    vector<int> v(n);
    for(auto &i : v)
        cin >> i;

    const int inf = 1e9;

    int wy = n + 1;

    REP(j, 2)
    {
        int tmp = 0;
        auto vv = v;
        REP(i, n - 1) {
            if(((i & 1) ^ j ? vv[i] <= vv[i + 1] : vv[i] >= vv[i + 1])) {
                ++tmp;
                vv[i + 1] = ((i & 1) ^ j ? -inf : inf);
            }
        }
        debug(tmp, vv);
        wy = min(wy, tmp);
    }

    cout << wy << endl;
}