#include <bits/stdc++.h>
using namespace std;
void optimise() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
}
long long int mod = 998244353;
void normalize(long long int &a) { a = (a + mod) % mod; }
long long int modmul(long long int a, long long int b) {
  a = a % mod;
  b = b % mod;
  normalize(a);
  normalize(b);
  return (a * b) % mod;
}
long long int modadd(long long int a, long long int b) {
  a = a % mod;
  b = b % mod;
  normalize(a);
  normalize(b);
  return (a + b) % mod;
}
long long int modsub(long long int a, long long int b) {
  a = a % mod;
  b = b % mod;
  normalize(a);
  normalize(b);
  return (a - b + mod) % mod;
}
long long int me(long long int x, long long int n) {
  x %= mod;
  if (n == 0) return 1;
  long long int u = me(x, n / 2) % mod;
  u = (u * u) % mod;
  if (n % 2) u = (u * x) % mod;
  return u;
}
long long int me1(long long int x, long long int n) {
  if (n == 0) return 1;
  long long int u = me1(x, n / 2);
  u = u * u;
  if (n % 2) u = u * x;
  return u;
}
inline long long int modInv(long long int a) { return me(a, mod - 2); }
inline long long int modDiv(long long int a, long long int b) {
  return modmul(a, modInv(b));
}
long long int __gcd(long long int a, long long int b) {
  if (b == 0)
    return a;
  else
    return __gcd(b, a % b);
}
void solve() {
  string s1;
  cin >> s1;
  string s2;
  cin >> s2;
  long long int a, b, c, d;
  a = (s1[0] - '0') * 10 + (s1[1] - '0');
  b = (s1[3] - '0') * 10 + (s1[4] - '0');
  c = (s2[0] - '0') * 10 + (s2[1] - '0');
  d = (s2[3] - '0') * 10 + (s2[4] - '0');
  long long int m = (c - a) * 60 + d - b;
  m /= 2;
  a += m / 60;
  b += m % 60;
  a += b / 60;
  b %= 60;
  if (a < 10)
    cout << 0 << a << ":";
  else
    cout << a << ":";
  if (b < 10)
    cout << 0 << b;
  else
    cout << b;
}
signed main() {
  optimise();
  long long int t;
  t = 1;
  cout << fixed << setprecision(10);
  while (t--) {
    solve();
  }
}
