#include <bits/stdc++.h>
using namespace std;
int dx[] = {+1, -1, +0, +0};
int dy[] = {+0, +0, +1, -1};
int fx[] = {+0, +0, +1, -1, -1, +1, -1, +1};
int fy[] = {-1, +1, +0, +0, +1, +1, -1, -1};
int hr[] = {-2, -2, -1, +1, +2, +2, -1, +1};
int hc[] = {+1, -1, +2, +2, -1, +1, -2, -2};
const int MAXN = (int)1e5 + 9;
int main() {
  int i, j, k, l, m, n, p, q, r, tc, t;
  int h1, m1, h2, m2, h3, m3;
  scanf("%d:%d", &h1, &m1);
  scanf("%d:%d", &h2, &m2);
  int mn = h2 * 60 + m2 - h1 * 60 - m1;
  mn /= 2;
  k = mn / 60;
  h1 += k;
  m1 += mn % 60;
  if (m1 > 59) {
    h1++;
    m1 = m1 - 60;
  }
  if (h1 <= 9)
    cout << "0" << h1;
  else
    cout << h1;
  cout << ":";
  if (m1 <= 9)
    cout << "0" << m1 << endl;
  else
    cout << m1 << endl;
  return 0;
}
