#include <bits/stdc++.h>
using namespace std;
void solve();
int main() {
  ios::sync_with_stdio(0);
  cin.tie(NULL);
  solve();
  return 0;
}
void solve() {
  string s1, s2;
  cin >> s1 >> s2;
  int sth, stm, enh, enm;
  sth = (s1[0] - 48) * 10 + (s1[1] - 48);
  stm = (s1[3] - 48) * 10 + (s1[4] - 48);
  enm = (s2[3] - 48) * 10 + (s2[4] - 48);
  enh = (s2[0] - 48) * 10 + (s2[1] - 48);
  int mid1 = (enh - sth) * 60;
  mid1 -= stm;
  mid1 += enm;
  mid1 /= 2;
  int ans1, ans2;
  int k = mid1 / 60;
  ans1 = sth + k;
  mid1 = mid1 % 60;
  if (stm + mid1 >= 60) {
    ans1++;
    mid1 -= (60 - stm);
    ans2 = mid1;
  } else {
    ans2 = stm + mid1;
  }
  if (ans1 < 10) {
    cout << 0 << ans1 << ":";
  } else {
    cout << ans1 << ":";
  }
  if (ans2 < 10) {
    cout << 0 << ans2 << "\n";
  } else {
    cout << ans2 << "\n";
  }
}
