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#include<bits/stdc++.h>

using namespace std;
#define ll long long
#define ld long double
#define pi pair<int,int>
#define vi vector<int>
#define vvi vector<vi>
#define vll vector<ll>
#define ST first
#define ND second
#define PB push_back

void Solve()
{
    int n;
    cin >> n;
    vi A(n);
    vi B(n);
    for(int i=0; i<n; ++i){
        cin >> A[i];
        B[i]=A[i];
    }
    int res1=0;
    for(int i=1; i<n; ++i)
    {
        if(i%2)
            if(B[i]<=B[i-1]){
                B[i]=1000'000'0;
                ++res1;
            }
        if(!(i%2))
            if(B[i]>=B[i-1]){
                B[i]=-1000'000'0;
                ++res1;
        }
    }
    int res2=0;
    for(int i=1; i<n; ++i)
    {
        if(i%2)
            if(A[i]>=A[i-1]){
                A[i]=-1000'000'0;
                ++res2;
                //cout << i << "\n";
            }
        if(!(i%2))
            if(A[i]<=A[i-1]){
                A[i]=1000'000'0;
                ++res2;
                //cout << i << "\n";
        }
    }
    cout << min(res1, res2) << "\n";
    //res2 mn<--->duzy start
    return;
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    int t;
    //cin >> t;
    t=1;
    while(t--)
    {
        Solve();
    }
    return 0;
}