#include <bits/stdc++.h>
using namespace std;
void display_vector(vector<int> v) {
  for (auto it = v.begin(); it != v.end(); it++) cout << *it << " ";
  cout << endl;
}
void speed() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
}
int main() {
  speed();
  char c, c1;
  int h, h1, h2, m, m1, m2;
  cin >> h >> c >> m;
  cin >> h1 >> c1 >> m1;
  int h_to_min = h * 60;
  int h1_to_min = h1 * 60;
  h2 = (m + m1 + h_to_min + h1_to_min) / 2;
  m2 = h2 % 60;
  h2 /= 60;
  if (h2 % 10 == h2 && m2 % 10 == m2)
    cout << 0 << h2 << ":" << 0 << m2 << endl;
  else if (h2 % 10 == h2)
    cout << 0 << h2 << ":" << m2 << endl;
  else if (m2 % 10 == m2)
    cout << h2 << ":" << 0 << m2 << endl;
  else
    cout << h2 << ":" << m2 << endl;
  return 0;
}
