task 184

#define loop(i,from,to) for (int i = from; i < to; ++i)
#include <bits/stdc++.h>

using std::cin;
using std::cout;
using std::endl;
using std::vector;
using std::string;
using std::tuple;
using std::set;

const int INF = 1e9+7;
const double eps = 1e-6;
template <typename T> void reverse(T &a) {
  long long s = a.size();
  for (long long i = 0; i < s / 2; ++i)
    std::swap(a[i], a[s - i - 1]);
}


signed main() {
  std::ios::sync_with_stdio(false);
  cin.tie(0);
  int t, n, dd, mm, h, m; cin >> n;
  vector<int> data;
  loop(i, 0, n) {
    scanf("%d.%d. %d:%d", &dd, &mm, &h, &m);
    t = m + h * 60 + dd * 24 * 60 + 1;
    for (int i = 2; i <= mm; ++i) {
      if (i - 1 == 1 || i - 1 == 3 || i - 1 == 5 || i - 1 == 7 || i - 1 == 8 || i - 1 == 10) t += 31 * 24 * 60;
      else if (i - 1 == 2) t += 28 * 24 * 60;
      else t += 30 * 24 * 60;
    }
    data.push_back(t);
  }
  int answ = 0;
  std::sort(data.begin(), data.end());
  for (int i = 0; i < n; i += 2)
    answ += data[i + 1] - data[i];
  cout << answ / 60 << ":" << answ % 60;
  //std::cout << "Hello World!\n";
  return 0;
}