26-45.cpp

#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#include <cmath>
using namespace std;

int main() {
    ifstream f("26-45.txt");
    int n;
    f >> n;

    vector<int> a(n);
    for (int i = 0; i < n; ++i) {
        f >> a[i];
    }

    sort(a.begin(), a.end());

    int k = 0, m = 0;

    for (int i = 0; i < n - 1; ++i) {
        for (int j = i + 1; j < n; ++j) {
            if ((a[i] + a[j]) % 2 == 0) {
                int s = (a[i] + a[j]) / 2;
                if (binary_search(a.begin(), a.end(), s)) {
                    ++k;
                    m = max(m, s);
                }
            }
        }
    }

    cout << k << " " << m << endl;

    return 0;
}