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#include<iostream>

using namespace std;
#define ll long long

const int maxx = 5e4+7;
ll a[maxx],b[maxx];
const ll pinf = 1e9;
const ll minf = -1e9;

int main()
{
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    int n; cin>>n;
    for(int i=0; n>i; i++)
    {
        int x; cin>>x;
        a[i] = b[i] = x;
    }
    int wyn = pinf;
    int pom = 0;
    for(int i=1; n>i; i++)
    {
        if(i%2==1)
        {
            if(a[i] >= a[i-1])
            {
                a[i] = minf;
                pom++;
            }
        }
        else
        {
            if(a[i] <= a[i-1])
            {
                a[i] = pinf;
                pom++;
            }
        }
    }
    wyn = min(wyn,pom);
    pom = 0;
    for(int i=1; n>i; i++)
    {
        if(i%2==0)
        {
            if(b[i] >= b[i-1])
            {
                b[i] = minf;
                pom++;
            }
        }
        else
        {
            if(b[i] <= b[i-1])
            {
                b[i] = pinf;
                pom++;
            }
        }
    }
    wyn = min(wyn,pom);
    cout<<wyn;
}
/*

5
4 1 3 3 1

4
-1000000 -1000000 -1000000 -1000000

*/