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#include<iostream>
using namespace std;
constexpr int maxN=100000+7;
int T[maxN];
int main(){
    ios_base::sync_with_stdio(0);
    int n;
    cin>>n;
    for (int i = 1; i <=n; i++)
    {
        cin>>T[i];
    }
    int res1=0;
    bool done[maxN]={false};
    for (int i = 1; i < n; i+=1)
    {
        if(done[i]){continue;;}
        if(i%2==1){
            if(T[i+1]<=T[i]){
                res1++;
                done[i+1]=true;
            }
        }else{
            if(T[i+1]>=T[i]){
                res1++;
                done[i+1]=true;
            }
        }
    }
    int res2=0;
    bool done2[maxN]={false};
    for (int i = 1; i < n; i+=1)
    {
        if(done2[i]){continue;;}
        if(i%2==1){
            if(T[i+1]>=T[i]){
                res2++;
                done2[i+1]=true;
            }
        }else{
            if(T[i+1]<=T[i]){
                res2++;
                done2[i+1]=true;
            }
        }
    }
    if(res1<res2){
        cout<<res1;
    }else{
        cout<<res2;
    }
    
    return 0;
}