#include <bits/stdc++.h>
using namespace std;
int main() {
  string s, e;
  cin >> s >> e;
  int strt = (s[0] - '0') * 10 + (s[1] - '0');
  int strt2 = (e[0] - '0') * 10 + (e[1] - '0');
  int end1 = (s[3] - '0') * 10 + (s[4] - '0');
  int end2 = (e[3] - '0') * 10 + (e[4] - '0');
  strt *= 60;
  strt += end1;
  strt2 *= 60;
  strt2 += end2;
  int res = (strt + strt2) / 2;
  if (res / 60 < 10)
    cout << "0" << res / 60 << ":";
  else
    cout << res / 60 << ":";
  if (res % 60 < 10)
    cout << "0" << res % 60;
  else
    cout << res % 60;
  cout << endl;
  return 0;
}
