#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    cin >> n;
    int a[n];
    for(int i = 0; i < n; i++){
        cin >> a[i];
    }
    int counter = 0;
    for(int i =0; i < n-1; i++){
        if(a[i] == 0 && a[i+1] == 1 || a[i] == 1 && a[i+1] == 0){
        counter++;
        i++;
        }
    }
    cout << counter;
}