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

int n, tone[50004], ans=50004;

set <int> S;
int peakL[50004], peakR[50004], valleyL[50004], valleyR[50004];

int main()
{ios_base::sync_with_stdio(0);
 cin.tie(0);
 cout.tie(0);

 cin >> n;
 for (int i=1; i<=n; i++){
    cin >> tone[i];
 	S.insert(tone[i]);
	}

 for (int i=2; i<=n; i++){
    if (tone[i]>tone[i-1] && (tone[i-1]<tone[i-2] || i==2)) peakL[i]=peakL[i-2];
    else peakL[i]=peakL[i-2]+1;

    if (tone[i]<tone[i-1] && (tone[i-1]>tone[i-2] || i==2)) valleyL[i]=valleyL[i-2];
    else valleyL[i]=valleyL[i-2]+1;
	}

 for (int i=n-1; i>0; i--){
	if (tone[i]>tone[i+1] && (tone[i+1]<tone[i+2] || i==n-1)) peakR[i]=peakR[i+2];
    else peakR[i]=peakR[i+2]+1;
		
    if (tone[i]<tone[i+1] && (tone[i-1]>tone[i-2] || i==n-1)) valleyR[i]=valleyR[i+2];
    else valleyR[i]=valleyR[i+2]+1;
    }


 for (int i=1; i<=n; i++)
	//cout <<i<<": peak="<<peakL[i]+peakR[i]<<" valley="<<valleyL[i]+valleyR[i]<<endl;
    ans=min(ans, min(peakL[i]+peakR[i], valleyL[i]+valleyR[i]));

 cout <<ans;
}
/*
5			1
4 1 3 3 1

4			2
1 1 1 1

6			1
2 1 3 7 6 9

9			2
4 2 0 2 1 3 7 6 9
*/