#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef long double ld;
typedef pair<ll, ll> par;
typedef vector<par> vpar;
typedef vector<bool> vbool;

#define forn(i, b, n) for (ll i = b; i < n; ++i)
#define vec vector
#define mp make_pair
#define add push_back
#define del pop_back
#define F first
#define S second
#define pw(x) (1ll << (x))
#define sqr(x) ((x)*(x))
#define all(x) (x).begin(), (x).end()

const ll INF = ll(1e18);
const ll MOD = ll(1e9) + 7;
const ll P = 259;
const ld EPS = 1e-10;

inline void error() {
	cout << "No";
	exit(0);
}

inline ll logn(ll n) {
	ll xx = ll(log2(ld(n)));
	return xx;
}

#define TASK ""

int source() {
    ll n;
    cin >> n;
    vll a(n);
    forn(i, 0, n) cin >> a[i];
    sort(all(a));
    ll ans = 0;
    forn(i, 0, n / 2 + (n % 2 == 0)) {
        ans += a[i] / 2 + (a[i] % 2 == 0);
    }
    cout << ans;
    return 0;
}

int main() {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
	srand(time(0));
	ios::sync_with_stdio(0);
	source();
	return 0;
}