#include <bits/stdc++.h>
using namespace std;
string str1, str2;
int main() {
  int i, m1, m2, h1, h2, carm, fm;
  cin >> str1 >> str2;
  m1 = m2 = h1 = h2 = 0;
  for (i = 3; i <= 4; i++) {
    m1 = m1 * 10 + str1[i] - '0';
    m2 = m2 * 10 + str2[i] - '0';
  }
  for (i = 0; i <= 1; i++) {
    h1 = h1 * 10 + str1[i] - '0';
    h2 = h2 * 10 + str2[i] - '0';
  }
  bool flagh, flagm;
  flagm = flagh = false;
  fm = (h1 + h2) * 30 + (m1 + m2) / 2;
  if (fm / 60 < 10) flagh = true;
  if (fm % 60 < 10) flagm = true;
  if (flagh) cout << "0";
  cout << fm / 60 << ":";
  if (flagm) cout << "0";
  cout << fm % 60 << "\n";
  return 0;
}
