#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef vector<ll> vl;
typedef pair<ll, ll> pl;
typedef long double ld;

#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define max(a, b) (a>b ? a : b)
#define min(a, b) (a<b ? a : b)
#define FAST ios::sync_with_stdio(0), cin.tie(0),cout.tie(0)


const int N = int(1e6) + 3;
const int MOD = int(1e9) + 7;

int n;
ll a[N];
int main() {
    FAST;
    //freopen("easy", "r", stdin);
    cin >> n;
    for(int i=0;i<n-1;i++){
        cin >> a[i];
        if(a[i]!=0){
            a[i]=2-a[i]%2;
        }
    }
    int bef=a[0];
    vector<int> v;
    v.pb(a[0]);
    for(int i=1;i<n-1;i++){
        if(a[i]==bef){
            continue;
        }
        v.pb(a[i]);
        bef=a[i];
    }
    int res=0;
    for(int i=1;i<v.size()-1;i++){
        if(v[i]==0){
            res++;
        }
    }
    vector<int> vv;
    for(int i=0;i<v.size();){
        if(v[i]==1){
            int j;
            for(j=i;j<v.size();j++){
                if(v[j]==0)
                    break;
            }
            vv.pb(j-i);
            i=j;
        }else{
            i++;
        }
    }
    for(auto u:vv){
        res+=(u+1)/2 - 1 ;
    }
    cout << res << endl;



    return 0;
}