#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  cerr.tie(nullptr);
  string s, t;
  cin >> s >> t;
  long long a =
      ((s[0] - '0') * 10 + (s[1] - '0')) * 60 + (s[3] - '0') * 10 + s[4] - '0';
  long long b =
      ((t[0] - '0') * 10 + (t[1] - '0')) * 60 + (t[3] - '0') * 10 + t[4] - '0';
  long long c = a + b;
  c /= 2;
  long long h = c / 60;
  long long m = c % 60;
  if (h <= 9) {
    cout << "0";
  }
  cout << h << ":";
  if (m <= 9) cout << "0";
  cout << m << '\n';
}
