#include <bits/stdc++.h>
using namespace std;
int main() {
  long long h1, m1, h2, m2, h3, m3, res = 0, a, b;
  char ch;
  cin >> h1 >> ch >> m1 >> h2 >> ch >> m2;
  a = h1 * 60 + m1;
  b = h2 * 60 + m2;
  res = (b - a) / 2;
  h3 = h1 + res / 60;
  m3 = m1 + res % 60;
  if (m3 >= 60) {
    m3 -= 60;
    h3++;
  }
  (h3 < 10) ? cout << 0 << h3 << ch : cout << h3 << ch;
  (m3 < 10) ? cout << 0 << m3 : cout << m3;
  return 0;
}
