#include<cstdio>
#include<algorithm>
#define rep(i,a) for(int i=0;i<(a);++i)

const int MAX_N = 100;

int N, A[MAX_N];
int ans;

int main()
{
	scanf( "%d", &N );
	rep( i, N )
	{
		scanf( "%d", A+i );
		
		if( i >= 2 && A[i-2] != A[i-1] && A[i-1] != A[i] && A[i-2] != A[i] )
		{
			int a[3] = { A[i-2], A[i-1], A[i] };
			std::sort( a, a+3 );

			if( A[i-2] == a[1] || A[i] == a[1] )
				++ans;
		}
	}

	printf( "%d\n", ans );

	return 0;
}