#include <bits/stdc++.h>
using namespace std;
const int dy[] = {-1, 0, 1, 0}, dx[] = {0, 1, 0, -1};
const double EPS = 1e-8;
const double PI = acos(-1.0);
int popcount(int n) { return __builtin_popcount(n); }
int popcount(long long n) { return __builtin_popcountll(n); }
template <class T>
int SIZE(T a) {
  return a.size();
}
template <class T>
string IntToString(T num) {
  string res;
  stringstream ss;
  ss << num;
  return ss.str();
}
template <class T>
T StringToInt(string str) {
  T res = 0;
  for (int i = 0; i < SIZE(str); i++) res = (res * 10 + str[i] - '0');
  return res;
}
template <class T>
T gcd(T a, T b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
template <class T>
T lcm(T a, T b) {
  return a / gcd(a, b) * b;
}
template <class T>
void PrintSeq(T &a, int sz) {
  for (int i = 0; i < sz; i++) {
    cout << a[i];
    if (sz == i + 1)
      cout << endl;
    else
      cout << ' ';
  }
}
long long getTen(int a) { return (a <= 0) ? 1 : (getTen(a - 1) * 10); }
bool EQ(double a, double b) { return abs(a - b) < EPS; }
void fastStream() {
  cin.tie(0);
  std::ios_base::sync_with_stdio(0);
}
vector<string> split(string str, char del) {
  vector<string> res;
  for (int i = 0, s = 0; i < SIZE(str); i++) {
    if (str[i] == del) {
      if (i - s != 0) res.push_back(str.substr(s, i - s));
      s = i + 1;
    } else if (i == SIZE(str) - 1) {
      res.push_back(str.substr(s));
    }
  }
  return res;
}
int N, K;
long long ary[100001];
int main() {
  cin >> N >> K;
  for (int i = 0; i < N; i++) {
    string s;
    cin >> s;
    vector<string> vs = split(s, '.');
    long long mask = 0;
    for (int j = 0; j < (int)vs.size(); j++) {
      long long num = StringToInt<int>(vs[j]);
      mask |= (num << ((3 - j) * 8));
    }
    ary[i] = mask;
  }
  long long subMask = 0;
  for (int i = 0; i < 32; i++) {
    subMask |= (1LL << (31 - i));
    set<long long> st;
    for (int j = 0; j < N; j++) {
      long long res = subMask & ary[j];
      st.insert(res);
    }
    if ((int)st.size() == K) {
      for (int j = 0; j < 4; j++) {
        int num = 0;
        for (int k = 0; k < 8; k++) {
          long long a = (subMask & (1LL << ((3 - j) * 8 + k))) > 0;
          num |= (a << k);
        }
        cout << num;
        if (j == 3)
          cout << endl;
        else
          cout << ".";
      }
      return 0;
    }
  }
  cout << -1 << endl;
  return 0;
}
