#include <bits/stdc++.h>
using namespace std;
template <typename T>
T pow(T a, T b, long long int m) {
  T ans = 1;
  while (b > 0) {
    if (b % 2 == 1) ans = (ans * a) % m;
    b /= 2;
    a = (a * a) % m;
  }
  return ans % m;
}
template <typename T>
void swap(T *a, T *b) {
  T temp = *a;
  *a = *b;
  *b = temp;
  return;
}
long long int toin(char a, char b) { return (a - '0') * 10 + (b - '0'); }
void solve() {
  long long int h1, h2, m1, m2;
  string a, b;
  cin >> a >> b;
  h1 = toin(a[0], a[1]);
  m1 = toin(a[3], a[4]);
  h2 = toin(b[0], b[1]);
  m2 = toin(b[3], b[4]);
  long long int len = 0;
  if (h1 <= h2)
    len = (h2 - h1) * 60;
  else
    len = (24 - h1 + h2) * 60;
  len = len - m1 + m2;
  len /= 2;
  long long int hr = len / 60;
  long long int mi = len % 60;
  h1 = (h1 + hr) % 24;
  m1 = m1 + mi;
  h1 = (h1 + m1 / 60) % 24;
  m1 = m1 % 60;
  if (h1 < 10) cout << 0;
  cout << h1 << ":";
  if (m1 < 10) cout << 0;
  cout << m1 << '\n';
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  solve();
  return 0;
}
