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

int arr[100005];
int brr[100005];

int main(){
    ios_base::sync_with_stdio(0);
    int n;
    cin>>n;
    for(int i=0;i<n;i++) cin>>arr[i];

    int res1 = 0;
    for(int i=0;i<n;i++) brr[i] = arr[i];
    for(int i=1;i<n;i++){
        int s = i&1;
        if(brr[i-1] >= brr[i]){
            if(s == 1) res1++, brr[i] = 1e9;
        }
        if(brr[i-1] <= brr[i]){
            if(s == 0) res1++, brr[i] = -1e9;
        }
    }

    int res2 = 0;
    for(int i=0;i<n;i++) brr[i] = arr[i];
    for(int i=1;i<n;i++){
        int s = (i+1)&1;
        if(brr[i-1] >= brr[i]){
            if(s == 1) res2++, brr[i] = 1e9;
        }
        if(brr[i-1] <= brr[i]){
            if(s == 0) res2++, brr[i] = -1e9;
        }
    }

    cout<<min(res1, res2)<<endl;
}