#include <stdio.h>


int main ( void ) {


	int N;
	scanf ( "%d" , &N );

	int Data [ 100 ];
	int SortedData [ 3 ];

	for ( int i = 0; i < N; i++ ) {
		scanf ( "%d" , Data + i );
	}

	int Count = 0;

	for ( int i = 0; ( i + 2 ) < N; i++ ) {

		SortedData [ 0 ] = Data [ i ];
		SortedData [ 1 ] = Data [ i + 1 ];
		SortedData [ 2 ] = Data [ i + 2 ];

		if ( SortedData [ 0 ] == SortedData [ 1 ] )continue;
		if ( SortedData [ 0 ] == SortedData [ 2 ] )continue;
		if ( SortedData [ 1 ] == SortedData [ 2 ] )continue;

		for ( int j = 0; j < 3; j++ ) {
			for ( int k = 0; k < 2; k++ ) {
				if ( SortedData [ k ] > SortedData [ k + 1 ] ) {
					int buf = SortedData [ k ];
					SortedData [ k ] = SortedData [ k + 1 ];
					SortedData [ k + 1 ] = buf;
				}
			}
		}

		if ( ( Data [ i ] == SortedData [ 1 ] ) || ( Data [ i + 2 ] == SortedData [ 1 ] ) ) {
			Count++;
		}

	}
	printf ( "%d\n" , Count );
	return 0;
}