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

int main()
{
	int n;
	cin >> n;
	long long A[n] , B[n];
	for(int i=0;i<n;i++)
	{
		cin >> A[i];
		B[i] = A[i];
	}
	
	
	int wyn1 = 0 , wyn2 = 0;
	for(int i=0;i<n-1;i++)
	{
		if(i%2==0)
		{
			if(B[i] <= B[i+1])
			{
				B[i+1] = -1000000009;
				wyn1++;
			}
		}
		else
		{
			if(B[i] >= B[i+1])
			{
				B[i+1] = 1000000009;
				wyn1++;
			}
		}
	}
	
	for(int i=0;i<n;i++)
	{
		B[i] = A[i];
	}
	
	for(int i=0;i<n-1;i++)
	{
		if(i%2==1)
		{
			if(B[i] <= B[i+1])
			{
				B[i+1] = -1000000009;
				wyn2++;
			}
		}
		else
		{
			if(B[i] >= B[i+1])
			{
				B[i+1] = 1000000009;
				wyn2++;
			}
		}
	}
	
	cout << min(wyn1,wyn2);
	return 0;
}