#include <iostream>
 
 
using namespace std;
 
const int NMAX = 32005 ;
 
int N, A[NMAX], sol ; 
 
int main() {
 
 
	cin >> N ;
 
	for(int i = 1 ; i <= N ; ++ i)
		cin >> A[i] ;
 
 
		for(int i = 1 ; i <= N ; ++ i)
			if(A[i] ==1 && A[i + 1] == 1)
			{
				A[++ i] = 0 ;
				++ sol ; 
			}
 
 
cout << sol ; 
	return 0;
}