package chelper;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import io.InputReader;
import io.OutputWriter;

public class GroupedWord {

  public void solve(int testNumber, InputReader in, OutputWriter out) {
    int n = in.nextInt();
    String[] a = in.nextStringArray(n);

    out.println(restore(a));
  }

  String restore(String[] a) {
    List<String> list = new ArrayList<>();
    Collections.addAll(list, a);

    for (char c = 'a'; c <= 'z'; c++) {
      List<String> interesting = new ArrayList<>();
      for (int i = 0; i < list.size();) {
        if (list.get(i).contains("" + c)) {
          interesting.add(list.get(i));
          list.remove(i);
        } else {
          i++;
        }
      }

      if (interesting.isEmpty()) {
        continue;
      }

      String result = combine(c, interesting);
      if (result == null) {
        return "IMPOSSIBLE";
      }
      list.add(result);
    }

    if (list.size() > 1) {
      return "MANY";
    }
    return list.get(0);
  }

  boolean isInvalid(String s) {
    for (int i = 0; i < s.length(); i++) {
      for (int j = i + 1; j < s.length(); j++) {
        if (s.charAt(i) == s.charAt(j) && s.charAt(i) != s.charAt(i + 1)) {
          return true;
        }
      }
    }
    return false;
  }

  String combine(char c, List<String> interesting) {
    List<String> only = new ArrayList<>();
    List<String> starts = new ArrayList<>();
    List<String> ends = new ArrayList<>();
    List<String> middle = new ArrayList<>();

    for (String s : interesting) {
      if (isInvalid(s)) {
        return null;
      }

      boolean doesStart = s.charAt(0) == c;
      boolean doesEnd = s.charAt(s.length() - 1) == c;

      if (doesStart) {
        if (doesEnd) {
          only.add(s);
        } else {
          starts.add(s);
        }
      } else {
        if (doesEnd) {
          ends.add(s);
        } else {
          middle.add(s);
        }
      }
    }

    if (starts.size() > 1 || ends.size() > 1 || middle.size() > 1) {
      return null;
    }

    if (!middle.isEmpty()) {
      if (only.isEmpty() && starts.isEmpty() && ends.isEmpty()) {
        return middle.get(0);
      } else {
        return null;
      }
    }

    StringBuilder sb = new StringBuilder();
    for (String s : ends) {
      sb.append(s);
    }
    for (String s : only) {
      sb.append(s);
    }
    for (String s : starts) {
      sb.append(s);
    }
    return sb.toString();
  }
}