#include <bits/stdc++.h>
using namespace std;
#define all(v) (v).begin(),(v).end()
#define pb(a) push_back(a)
#define rep(i, n) for(int i=0;i<n;i++)
#define foa(e, v) for(auto& e : v)
using ll = long long;
const ll MOD7 = 1000000007, MOD998 = 998244353, INF = (1LL << 60);
#define dout(a) cout<<fixed<<setprecision(10)<<a<<endl;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;vector<int> cnt(n, 0);
    rep(i, n) {
        int a; cin >> a;
        cnt[a - 1] ++;
    } 
    int sum = 0;
    rep(i, n) if(cnt[i] & 1) sum ++;
    cout << (n - sum) / 2 << endl;
    return 0;
}