#include <bits/stdc++.h>
using namespace std;
int modInverse(int a, int m);
int gcd(int a, int b);
int power(int x, unsigned int y, unsigned int m);
int gcd(int a, int b) {
  if (a == 0) return b;
  return gcd(b % a, a);
}
int power(int x, unsigned int y, unsigned int m) {
  if (y == 0) return 1;
  int p = power(x, y / 2, m) % m;
  p = (p * p) % m;
  return (y % 2 == 0) ? p : (x * p) % m;
}
int modInverse(int a, int m) {
  int m0 = m;
  int y = 0, x = 1;
  if (m == 1) return 0;
  while (a > 1) {
    int q = a / m;
    int t = m;
    m = a % m, a = t;
    t = y;
    y = x - q * y;
    x = t;
  }
  if (x < 0) x += m0;
  return x;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  string s1, s2;
  cin >> s1 >> s2;
  int h1, h2, m1, m2;
  h1 = stoi(s1.substr(0, 2));
  m1 = stoi(s1.substr(3, 2));
  h2 = stoi(s2.substr(0, 2));
  m2 = stoi(s2.substr(3, 2));
  int m, h;
  m = ((h1 * 60 + m1 + h2 * 60 + m2) / 2) % 60;
  h = ((h1 * 60 + m1 + h2 * 60 + m2) / 2) / 60;
  if (h < 10) cout << '0';
  cout << h << ':';
  if (m < 10) cout << '0';
  cout << m;
  return 0;
}
