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#include <bits/stdc++.h>
using namespace std;

constexpr int MAXN = 50004;
constexpr int oo = 1000000000;

int c[MAXN];
int ct[MAXN];

int main(){
    int n;
    cin >> n;
    for(int i = 1; i <= n; i++){
        cin >> c[i];
    }

    int r1 = 0;
    ct[1] = c[1];
    for(int i = 2; i <= n; i++){
        ct[i] = c[i];
        if ( ct[i-1] == ct[i] || ((i % 2) ^ (ct[i-1] < ct[i]) )){
            r1++;
            ct[i] = 2*oo*(i%2) - oo;       
        }
    }

    int r2 = 0;
    ct[1] = c[1];
    for(int i = 2; i <= n; i++){
        ct[i] = c[i];
        if ( ct[i-1] == ct[i] || (!(i % 2) ^ (ct[i-1] < ct[i]) )){
            r2++;
            ct[i] = 2*oo*(!(i%2)) - oo;       
        }
    }

    cout  << min(r1, r2)  << '\n';

    
}