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#include <iostream>
#include <algorithm>
using namespace std;

int main() {
    int N,ansA,ansB,INF;
    ansA = ansB = 0;
    INF = 1 << 22;
    int a[50000],b[50000],c;
    cin>>N;
    for(int i=0; i<N; ++i) {
        cin>>c;
        a[i] = b[i] = c;
    }
    for(int i=1; i<N; ++i) {
        //pierwszy wiekszy
        if(i % 2 == 1) {
            if(a[i] >= a[i-1]) {
                ansA++;
                a[i] = -INF;
            }
        }
        if(i % 2 == 0) {
            if(a[i] <= a[i-1]) {
                ansA++;
                a[i] = INF;
            }
        }
    }
    
    for(int i=1; i<N; ++i) {
        //pierwszy mniejszy
        if(i % 2 == 1) {
            if(b[i] <= b[i-1]) {
                ansB++;
                b[i] = INF;
            }
        }
        if(i % 2 == 0) {
            if(b[i] >= b[i-1]) {
                ansB++;
                b[i] = -INF;
            }
        }
    }
    
    int ans = min(ansA,ansB);
    cout<<ans<<endl;
    
    return 0;
}