#include <bits/stdc++.h>
using namespace std;
int main() {
  int a, b, c, d, r;
  char ch;
  cin >> a >> ch >> b;
  cin >> c >> ch >> d;
  r = ((a + c) * 60 + (b + d)) / 2;
  cout << setfill('0') << setw(2) << r / 60 << ch << setfill('0') << setw(2)
       << r % 60 << endl;
  return 0;
}
