#include "bits/stdc++.h"

#pragma GCC optimize("Ofast")
#pragma GCC optimize("-O2")

using namespace std;
using ll = long long;
using ld = long double;

int dx[] = {1, -1, 0, 0, -1, -1, 1, 1};
int dy[] = {0, 0, 1, -1, -1, 1, -1, 1};

const int N = 2E5 + 5, M = 2E6 + 10, MOD = 1E9 + 7, OO = 0x3f3f3f3f;;
int n, a[N], ans;

int main() {
    ios_base::sync_with_stdio(0), cin.tie(0);
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
#endif /*ONLINE_JUDGE*/

    cin >> n;
    for (int i = 0; i < n; ++i) cin >> a[i];

    for (int i = 0; i+1 < n; ++i) {
        if(a[i]+a[i+1] == 1) ans++, i++;
    }

    cout << ans;
    
    return 0;
}