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

constexpr int high = 1e9;
constexpr int low = -1e9;
constexpr int M = 5e4+7;

int a[M], b[M];

int main(){
	ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
	
	int n, rm = 0, mr = 0;
	
	cin >> n;
	
	for(int i=0; i<n; i++){
		cin >> a[i];
		b[i] = a[i];
	}
	
	//rosnie --> maleje --> rosnie np. 1 3 1 3
	for(int i=1; i<n; i++){
		if(i % 2){
			if(a[i] <= a[i-1]){
				a[i] = high;
				rm++;
			}
		}
		else{
			if(a[i] >= a[i-1]){
				a[i] = low;
				rm++;
			}
		}
	}
	
	//maleje --> rosnie --> maleje np. 3 1 3 1
	for(int i=1; i<n; i++){
		if(i % 2 == 0){
			if(b[i] <= b[i-1]){
				b[i] = high;
				mr++;
			}
		}
		else{
			if(b[i] >= b[i-1]){
				b[i] = low;
				mr++;
			}
		}
	}
	
	cout << min(rm, mr) << '\n';
	
	return 0;
}