#include <bits/stdc++.h>
using namespace std;
const long long MXN = 3e5 + 1;
const long long MwOD = 1e9 + 7;
long long x, x1, m, m1;
string s, s1;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> s >> s1;
  string t;
  stringstream ss;
  t += s[0];
  t += s[1];
  ss << t;
  ss >> x;
  string t1;
  stringstream sss;
  t1 += s1[0];
  t1 += s1[1];
  sss << t1;
  sss >> x1;
  string l;
  stringstream ssss;
  l += s[3];
  l += s[4];
  ssss << l;
  ssss >> m;
  string l1;
  stringstream sssss;
  l1 += s1[3];
  l1 += s1[4];
  sssss << l1;
  sssss >> m1;
  long long all1 = x * 60 + m;
  long long all2 = x1 * 60 + m1;
  long long k = all1 + all2;
  long long r = k / 2;
  if ((r / 60) / 10 == 0) {
    cout << '0' << r / 60 << ':';
    if ((r % 60) / 10 == 0) {
      cout << '0' << r % 60;
    } else {
      cout << r % 60;
    }
  } else {
    cout << r / 60 << ':';
    if ((r % 60) / 10 == 0) {
      cout << '0' << r % 60;
    } else {
      cout << r % 60;
    }
  }
  return 0;
}
