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#include <bits/stdc++.h>
using namespace std;
#define X first
#define Y second
#define ii pair<int, int>
#define ll long long


int n, a[50007], b[50007], counter1, counter2;
//Autor:    Jakub Wielocha
//          VI LO Radom
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cin>>n;
    for(int i = 1;i<=n;i++)
        cin>>a[i];

    for(int i = 1;i<=n;i++)
        b[i] = a[i];

    for(int i = 2;i<=n;i++)
        if(i%2==0)
        {
            if(a[i-1]>=a[i])
                counter1++, a[i] = 1e9;
        }
        else
        {
            if(a[i-1]<=a[i])
                counter1++, a[i] = -1e9;
        }

    for(int i = 2;i<=n;i++)
        if(i%2==1)
        {
            if(b[i-1]>=b[i])
                counter2++, b[i] = 1e9;
        }
        else
        {
            if(b[i-1]<=b[i])
                counter2++, b[i] = -1e9;
        }
    cout<<min(counter1, counter2)<<"\n";
    return 0;
}