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#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;

int a[50009];
int temp[50009];
constexpr int oo=1'000'000'009;

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int n,best,odp;
    cin >> n;
    for (int x=0;x<n;x++){
        cin >> a[x];
        temp[x] = a[x];
    }
    best = n;
    for (int typ=0;typ<2;typ++){
        odp = 0;
        for (int x=0;x<n-1;x++){
            if (x%2==typ){
                if (temp[x] >= temp[x+1]){
                    temp[x+1] = oo;
                    odp += 1;
                }
            }
            else{
                if (temp[x] <= temp[x+1]){
                    temp[x+1] = -oo;
                    odp += 1;
                }
            }
        }
        for (int x=0;x<=n;x++){
            temp[x] = a[x];
        }
        best = min(odp,best);
    }
    cout << best << '\n';
    return 0;
}