#include<iostream>
#include<vector>
using namespace std;
int main() {
	int N,count=0;
	cin >> N;
	vector<int> v(N);
	for (int i = 0; i < N; i++) {
		cin >> v[i];
	}
	for (int i = 0; i < N - 2; i++) {
		if (v[i] != v[i + 1] && v[i + 1] != v[i + 2] && v[i+2]!=v[i]) {
			count++;
		}
	}
	cout << count << "\n";
	return 0;
}