#include <bits/stdc++.h>
using namespace std;
long long int mod(long long int x) {
  return (((x) % 1000000007) + 1000000007) % 1000000007;
}
long long int solve() {
  string s, t;
  cin >> s >> t;
  string s1 = "00", s2 = "00", t1 = "00", t2 = "00";
  s1[0] = s[0];
  s1[1] = s[1];
  s2[0] = s[3];
  s2[1] = s[4];
  t1[0] = t[0];
  t1[1] = t[1];
  t2[0] = t[3];
  t2[1] = t[4];
  long long int a, b, c, d;
  stringstream geek(s1);
  geek >> a;
  stringstream geek2(s2);
  geek2 >> b;
  stringstream geek3(t1);
  geek3 >> c;
  stringstream geek4(t2);
  geek4 >> d;
  long long int min = d + c * 60 - (b + a * 60);
  min /= 2;
  long long int h = min / 60;
  long long int g = min % 60;
  a = a + h;
  b = b + g;
  if (b >= 60) {
    a++;
    b = b % 60;
  }
  if (a > 23) {
    a = a % 24;
  }
  cout << setfill('0') << setw(2) << a << ":" << setfill('0') << setw(2) << b
       << "\n";
  return 0;
}
signed main() {
  ios::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
  long long int t;
  t = 1;
  while (t--) {
    solve();
  }
  return 0;
}
