#include <bits/stdc++.h>
using namespace std;
int main() {
  int h1, m1, h2, m2;
  scanf("%d:%d", &h1, &m1);
  scanf("%d:%d", &h2, &m2);
  int u = h1 * 60 + m1;
  int v = h2 * 60 + m2;
  int w = (u + v) / 2;
  printf("%02d:%02d\n", w / 60, w % 60);
}
