#include <bits/stdc++.h>
using namespace std;
int h1, m1, h2, m2;
int t1, t2;
int main() {
  char c;
  scanf("%d", &h1);
  scanf("%c", &c);
  scanf("%d", &m1);
  scanf("%d", &h2);
  scanf("%c", &c);
  scanf("%d", &m2);
  t1 = h1 * 60 + m1;
  t2 = h2 * 60 + m2;
  int med = (t1 + t2) / 2;
  int ansH = med / 60;
  int ansM = med - (ansH * 60);
  if (ansH / 10 == 0 && ansM / 10 == 0) {
    printf("0%d:0%d\n", ansH, ansM);
  } else if (ansH / 10 == 0) {
    printf("0%d:%d\n", ansH, ansM);
  } else if (ansM / 10 == 0) {
    printf("%d:0%d\n", ansH, ansM);
  } else {
    printf("%d:%d\n", ansH, ansM);
  }
}
