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#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n, res1 = 0, res2 = 0, res3 = 0, res4 = 0;
	cin >> n;
	vector <int> a (n);
	for(int i = 0; i<n; ++i)
	{
		cin >> a[i];
	}
	for(int i = 1; i < n; i += 2)
	{
		if((i+1 < n) and (a[i] >= a[i-1] or a[i] >= a[i+1]))
			res1++;
		if((i+1 < n) and (a[i] <= a[i-1] or a[i] <= a[i+1]))
			res2++;
		if(i+1 == n)
		{
			if(a[i] >= a[i-1])
				res1++;
			if(a[i] <= a[i-1])
				res2++;
		}
	}
	if(a[0] <= a[1])
                        res4++;
        if(a[0] >= a[1])
                        res3++;  
	if(a[n-1] <= a[n-2])
			res4++;
	if(a[n-1] >= a[n-2])
			res3++;
	for(int i = 2; i < n; i+=2)
	{
		if((i+1 < n) and (a[i] >= a[i-1] or a[i] >= a[i+1]))
                        res3++;
                if((i+1 < n) and (a[i] <= a[i-1] or a[i] <= a[i+1]))
                        res4++;

	}

	if(res1 <= res2 and res1 <= res3 and res1 <= res4)
		cout << res1;//<< " 1";
	else if(res2 <= res1 and res2 <= res3 and res2 <= res4)
		cout << res2;//<< " 2 ";
	else if(res3 <= res1 and res3 <= res2 and res3 <= res4)
		cout << res3;//<< " 3 ";
	else
		cout << res4;//<< " 4 ";
	return 0;
}