#include <bits/stdc++.h>
using namespace std;

#define ll long long int
#define ld long double
#define endl '\n'
#define fasterio ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
#define yes cout << "YES" << endl
#define no cout << "NO" << endl

void solve() {
    // Your code here
    ll n;
    cin>>n;
    vector<ll> v(n);
    for(ll i=0;i<n;i++) cin>>v[i];

    ll count=0,sum=0;
    for(ll i=0;i<n;i++) {
        sum+=v[i];
        if(sum%2==0) {
            count++;
            sum=0;
        }
    }
    if(n==1){
        cout<<-1<<endl;
    }else{
        cout<<count<<endl;
    
    }
}

int main() {
    fasterio;
    // Always use ll, int may give TLE
    ll t;
    // cin >> t;
    t=1;
    while (t--) {
        solve();
    }
    return 0;
}