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#include<iostream>
#include<vector>
using namespace std;

bool rel(int a,int b,int c)
{
    if(c) return a>b;
    return b>a;
}

int main()
{
    ios_base::sync_with_stdio(0);
    int n;
    cin >> n;
    vector<int> T(n);
    for (auto& i : T) cin >> i;
    int result1 = 0, result2 = 0;
    vector<int> A=T;
    for(int i=0 ; i<n-1 ; i++)
    {
        if(!rel(A[i],A[i+1],i%2))
        {
            if(i%2==0)A[i+1]=1e9;
            else A[i+1]=-1e9;
            result1++;
        }
    }
    A=T;
    for(int i=0 ; i<n-1 ; i++)
    {
        if(!rel(A[i],A[i+1],(i+1)%2))
        {
            if(i%2==1)A[i+1]=1e9;
            else A[i+1]=-1e9;
            result2++;
        }
    }
    cout<<min(result1,result2)<<endl;
    /*for (int i = 1; i < T.size() - 1; i += 2)
    {
        if (T[i] >= T[i - 1] || T[i] >= T[i + 1]) result1++;
        if (T[i] <= T[i - 1] || T[i] <= T[i + 1]) result2++;
    }
    if (n % 2 == 0 && T[n - 1] <= T[n - 2]) result1++;
    if (n % 2 == 0 && T[n - 1] >= T[n - 2]) result2++;
    int result3 = 0, result4 = 0;

    if (T[1] <= T[0]) result3++;
    if (T[1] >= T[0]) result4++;

    for (int i = 2; i < T.size() - 1; i += 2)
    {
        if (T[i] >= T[i - 1] || T[i] >= T[i + 1]) result3++;
        if (T[i] <= T[i - 1] || T[i] <= T[i + 1]) result4++;
    }
    if (n % 2 == 1 && T[n - 1] >= T[n - 2]) result3++;
    if (n % 2 == 1 && T[n - 1] <= T[n - 2]) result4++;
    cout << min(min(result1, result2), min(result4, result3)) << "\n";*/
    return 0;
}