#include <bits/stdc++.h>
using namespace std;
int main() {
  string s1, s2;
  cin >> s1 >> s2;
  int h1 = stoi(s1.substr(0, 2));
  int m1 = stoi(s1.substr(3, 2));
  int h2 = stoi(s2.substr(0, 2));
  int m2 = stoi(s2.substr(3, 2));
  int m3 = (m1 + m2) / 2;
  int h3 = h1 + h2;
  if (h3 % 2 != 0) m3 += 30;
  h3 = h3 / 2;
  if (m3 >= 60) {
    h3++;
    m3 -= 60;
  }
  if (h3 < 10) cout << "0";
  cout << h3 << ":";
  if (m3 < 10) cout << "0";
  cout << m3;
}
