#include <bits/stdc++.h>
using namespace std;
long long a, b, c, d, n, m, l, x, y;
string s, v;
int main() {
  cin >> s >> v;
  a = 10 * (int(s[0]) % 48) + int(s[1]) % 48;
  b = 10 * (int(s[3]) % 48) + int(s[4]) % 48;
  c = 10 * (int(v[0]) % 48) + int(v[1]) % 48;
  d = 10 * (int(v[3]) % 48) + int(v[4]) % 48;
  n = 60 * a + b;
  m = 60 * c + d;
  l = (n + m) / 2;
  y = l % 60;
  x = l / 60;
  if (x < 10 && y < 10) {
    cout << 0 << x << ":" << 0 << y;
    return 0;
  } else if (x < 10) {
    cout << 0 << x << ":" << y;
    return 0;
  } else if (y < 10) {
    cout << x << ":" << 0 << y;
    return 0;
  }
  cout << x << ":" << y;
}
