#include <bits/stdc++.h>
using namespace std;
using namespace std;
long long gcd(long long a, long long b) {
  if (a < b)
    return gcd(b, a);
  else if (b == 0)
    return a;
  else
    return gcd(b, a % b);
}
long long lcm(long long a, long long b) { return a * b / gcd(a, b); }
long long pow(long long b, long long e) {
  if (e == 0)
    return 1;
  else if (e % 2 == 0) {
    long long a = pow(b, e / 2);
    return a * a;
  } else {
    long long a = pow(b, e / 2);
    return b * a * a;
  }
}
long long pow_m(long long x, long long y, long long m = 1000000007) {
  x = x % m;
  long long res = 1;
  while (y) {
    if (y & 1) res = res * x;
    res %= m;
    y = y >> 1;
    x = x * x;
    x %= m;
  }
  return res;
}
long long modInverse(long long a, long long m) { return pow_m(a, m - 2, m); }
long long max(long long a, long long b) {
  if (a >= b)
    return a;
  else
    return b;
}
long long min(long long a, long long b) {
  if (a <= b)
    return a;
  else
    return b;
}
long long bin_coff(long long n, long long k, long long m) {
  vector<vector<long long>> ans(n + 1, vector<long long>(k, 0));
  for (long long i = 0; i < n + 1; i++) {
    for (long long j = 0; j < min(i, k) + 1; j++) {
      if (j == 0 || j == i)
        ans[i][j] = 1;
      else
        ans[i][j] = ans[i - 1][j - 1] % m + ans[i - 1][j] % m;
    }
  }
  return ans[n][k] % m;
}
long long inverse(long long i) {
  if (i == 1) return 1;
  return (1000000007 -
          ((1000000007 / i) * inverse(1000000007 % i)) % 1000000007 +
          1000000007) %
         1000000007;
}
const long long N = 10000007;
vector<bool> primes(N + 1, true);
void eren() {
  primes[0] = false;
  primes[1] = false;
  for (long long i = 2; i * i <= N; i++) {
    if (primes[i]) {
      for (long long j = i * i; j <= N; j += i) primes[j] = false;
    }
  }
}
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  eren();
  int tt = 1;
  for (int it = 0; it < tt; it++) {
    long long n;
    cin >> n;
    string s;
    cin >> s;
    for (long long i = 0; i < n - 1; i++) {
      string t;
      cin >> t;
      for (long long j = 0; j < t.length(); j++) {
        if (t[j] == '?') {
        } else {
          if (s[j] == '?')
            s[j] = t[j];
          else if (s[j] == t[j]) {
          } else
            s[j] = '*';
        }
      }
    }
    for (long long i = 0; i < s.length(); i++) {
      if (s[i] == '?')
        s[i] = 'a';
      else if (s[i] == '*')
        s[i] = '?';
    }
    cout << s << "\n";
  }
  return 0;
}
