#include <bits/stdc++.h>
using namespace std;
int n;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  string s1, s2;
  cin >> s1 >> s2;
  int h1, h2, m1, m2;
  string x = "";
  x = s1.substr(0, 2);
  h1 = stoi(x);
  x = s1.substr(3, 2);
  m1 = stoi(x);
  x = s2.substr(0, 2);
  h2 = stoi(x);
  x = s2.substr(3, 2);
  m2 = stoi(x);
  if (h1 <= h2) {
    int dif = (h2 - h1) * 60 + m2 - m1;
    dif /= 2;
    m1 += dif;
    dif = m1 / 60;
    m1 %= 60;
    h1 += dif;
    if (h1 < 10) cout << "0";
    cout << h1 << ":";
    if (m1 < 10) cout << "0";
    cout << m1;
  } else {
    h2 += 24;
    int dif = (h2 - h1) * 60 + m2 - m1;
    dif /= 2;
    m1 += dif;
    dif = m1 / 60;
    m1 %= 60;
    h1 += dif;
    h1 %= 24;
    if (h1 < 10) cout << "0";
    cout << h1 << ":";
    if (m1 < 10) cout << "0";
    cout << m1;
  }
  return (0);
}
