#include <bits/stdc++.h>
using namespace std;
const int maxn = 100;
const int mod = 1e9 + 7;
const double pi = acos(-1.0);
int main() {
  int h1, h2, m1, m2;
  char c1, c2;
  while (scanf("%d %c %d %d %c %d", &h1, &c1, &m1, &h2, &c2, &m2) != EOF) {
    int sum_h = h1 + h2;
    int sum_m = m1 + m2;
    if (sum_m >= 60) {
      sum_h++;
      sum_m -= 60;
    }
    if (sum_h % 2 == 1) {
      sum_h--;
      sum_m += 60;
    }
    sum_h /= 2;
    sum_m /= 2;
    if (sum_m >= 10 && sum_h >= 10)
      printf("%d:%d\n", sum_h, sum_m);
    else if (sum_m >= 10 && sum_h < 10)
      printf("0%d:%d\n", sum_h, sum_m);
    else if (sum_m < 10 && sum_h >= 10)
      printf("%d:0%d\n", sum_h, sum_m);
    else
      printf("0%d:0%d\n", sum_h, sum_m);
  }
  return 0;
}
