#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  string s1, s2;
  cin >> s1 >> s2;
  long long n1 = ((s1[0] - '0') * 10 + (s1[1] - '0')) * 60 +
                 (s1[3] - '0') * 10 + (s1[4] - '0');
  long long n2 = ((s2[0] - '0') * 10 + (s2[1] - '0')) * 60 +
                 (s2[3] - '0') * 10 + (s2[4] - '0');
  long long n = (n1 + n2) / 2;
  if (n / 60 < 10) cout << "0";
  cout << n / 60 << ":";
  if (n % 60 < 10) cout << "0";
  cout << n % 60 << endl;
  return 0;
}
