#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (ll i = 0; i < (n); ++i)

int main() {
    ll A, B, C;
    cin >> A >> B >> C;
    if (abs(B - A) > C) {
        cout << min(A, B) + C << endl;
        return 0;
    }
    cout << (A + B + C) / 2 << endl;
}