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#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define st first
#define nd second
#define pb push_back
#define mp make_pair
#define rep(i,a,b) for(ll i=(ll)a;i<=(ll)b;++i)
#define all(a) a.begin(),a.end()
#define sz(x) (int)(x).size()
const int mxN = 5e4+7, INF = 1e9;
int b[mxN], a[mxN];

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n; cin >> n;
    rep(i,1,n) cin >> a[i];
    rep(i,1,n) b[i] = a[i];
    int res0=0,res1=0;
    rep(i,2,n){
        if(i%2==0 && b[i-1] >= b[i]) b[i] = INF, res0++;
        if(i%2==1 && b[i-1] <= b[i]) b[i] = -INF, res0++;
    }
    rep(i,1,n) b[i] = a[i];
    rep(i,2,n){
        if(i%2==0 && b[i-1] <= b[i]) b[i] = -INF, res1++;
        if(i%2==1 && b[i-1] >= b[i]) b[i] = INF, res1++;
    }
    cout << min(res0,res1) << "\n";
}