#include <bits/stdc++.h>
using namespace std;
int h1, h2, m1, m2;
int minutes;
int main(void) {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  scanf("%d:%d", &h1, &m1);
  scanf("%d:%d", &h2, &m2);
  minutes = h1 * 60 + m1 + h2 * 60 + m2;
  minutes /= 2;
  printf("%02d:%02d\n", minutes / 60, minutes % 60);
  return 0;
}
