#include <bits/stdc++.h>
using namespace std;
template <class T>
ostream& operator<<(ostream& os, vector<T> V) {
  os << "[ ";
  for (auto v : V) os << v << " ";
  return os << "]";
}
template <class L, class R>
ostream& operator<<(ostream& os, pair<L, R> P) {
  return os << "(" << P.first << "," << P.second << ")";
}
const long long Mod = 1e9 + 7;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  string a, b;
  cin >> a >> b;
  int h1 = stoi(a.substr(0, 2));
  int m1 = stoi(a.substr(3, 2));
  int h2 = stoi(b.substr(0, 2));
  int m2 = stoi(b.substr(3, 2));
  int h = (h1 + h2) * 30 + (m1 + m2) / 2;
  if (h / 600 == 0) cout << "0";
  cout << h / 60 << ":";
  if ((h % 60) / 10 == 0) cout << "0";
  cout << h % 60 << endl;
  return 0;
}
