#include <bits/stdc++.h>
using namespace std;
int presum[100005];
int main() {
  ios::sync_with_stdio(0), cin.tie(0);
  int h1, m1, h2, m2;
  char c1, c2;
  cin >> h1 >> c1 >> m1 >> h2 >> c2 >> m2;
  int x = h1 * 60 + m1;
  int y = h2 * 60 + m2;
  int ans = (x + y) / 2;
  if (ans / 60 <= 9) {
    cout << "0" << ans / 60 << ":";
  }
  if (ans / 60 >= 10) {
    cout << ans / 60 << ":";
  }
  if (ans % 60 <= 9) {
    cout << "0" << ans % 60 << endl;
  }
  if (ans % 60 >= 10) {
    cout << ans % 60 << endl;
  }
  return 0;
}
