#include <bits/stdc++.h>
using namespace std;
int main() {
  string s, e;
  cin >> s >> e;
  int h1, m1, h2, m2;
  h1 = (s[0] - '0') * 10 + (s[1] - '0');
  h2 = (e[0] - '0') * 10 + (e[1] - '0');
  m1 = (s[3] - '0') * 10 + (s[4] - '0');
  m2 = (e[3] - '0') * 10 + (e[4] - '0');
  long long int total1 = h1 * 60 + m1;
  long long int total2 = h2 * 60 + m2;
  long long int dif = (total2 - total1) / 2;
  int ansh = dif / 60;
  int ansm = dif % 60;
  int fh = h1 + ansh;
  int fm = m1 + ansm;
  if (fm >= 60) {
    fh += 1;
    fm %= 60;
  }
  if (fh > 9) {
    cout << fh << ":";
  } else {
    cout << "0" << fh << ":";
  }
  if (fm > 9) {
    cout << fm << endl;
  } else {
    cout << "0" << fm << endl;
  }
}
