#include <bits/stdc++.h>
using namespace std;
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int n, a[50000], changes = 0;
int even = 0, odd = 0; // amnt of: even - a[2n] > a[2n-1]; odd - a[2n+1] > a[2n]; n1 = 1
bool asc = 1;
cin >> n;
for (int i=0; i<n; i++)
cin >> a[i];
for (int i=0; i<n-1; i++) {
if (a[i+1] != a[i]) {
if ((a[i+1] > a[i] && i%2 == 0) || (a[i+1] < a[i] && i%2 == 1))
even++;
else
odd++;
}
}
if (odd > even)
asc = 0;
int i=0;
while (i+1<n) {
if (asc && a[i+1] <= a[i]) {
changes++; i++;
}
else if (!asc && a[i+1] >= a[i]) {
changes++; i++;
}
else {
if (asc) asc = 0;
else asc = 1;
}
i++;
}
cout << changes;
}