import java.util.*; import java.io.*; import java.math.*; import java.util.stream.*; import java.util.function.*; class Main { public final PrintWriter out = new PrintWriter(System.out); public final FastScanner in = new FastScanner(); public static final int inf = (1 << 30) ; public static final long lnf = (1L << 30); public boolean dbg = false ; public void solve() { int n = in.nextInt(); Map memo = new HashMap<>(); for(int i = 0 ; i < n ; i ++) { String s = in.next(); List ss = new ArrayList<>(); for(int j = 0 ; j < s.length() ; j ++) ss.add(s.charAt(j)); Collections.sort(ss); StringBuilder sb = new StringBuilder(); for(char c : ss) sb.append(c); String res = sb.toString(); memo.put(res , memo.getOrDefault(res , 0) + 1); } String ans = null ; for(String str : memo.keySet()) if(memo.get(str) != 2) ans = str ; out.println(ans == null ? -1 : ans + 'a'); out.flush(); } public static void main(String [] args) { new Main().solve(); } } final class Utils { public static final int [] dy4 = {-1, 0, 1, 0} , dx4 = {0, 1, 0, -1} ; public static final int [] dy8 = {-1, -1, -1, 0, 1, 1, 1, 0} , dx8 = {-1, 0, 1, 1, 1, 0, -1, -1} ; public boolean isNumber(char c) { return '0' <= c && c <= '9'; } public boolean isNumber(String s) { for(int i = 0 ; i < s.length() ; i ++) if(!isNumber(s.charAt(i))) return false; return true ; } public boolean isInclude(int l , int r , int L , int R) { return (L <= l && r <= R) ; } public boolean isInclude_2D(int y , int x , int h , int w) { return (0 <= y && y < h) && (0 <= x && x < w); } public char Character_shift(char c , int s) { if('a' <= c && c <= 'z') return (char) (((((c - 'a') + s) % 26) + 26) % 26 + 'a'); if('A' <= c && c <= 'Z') return (char) (((((c - 'A') + s) % 26) + 26) % 26 + 'A'); if('0' <= c && c <= '9') return (char) (((((c - '0') + s) % 10) + 10) % 10 + '0'); return 'c'; } // ボクシング用 public Integer [] toInteger(int [] a) { return Arrays.stream(a).boxed().toArray(Integer[]::new); } public Long [] toLong(long [] a) { return Arrays.stream(a).boxed().toArray(Long[]::new); } public Double [] toDouble(double [] a) { return Arrays.stream(a).boxed().toArray(Double[]::new); } public List ArrayList(T [] a) { return Arrays.stream(a).collect(Collectors.toCollection(ArrayList::new)); } public HashSet HashSet(T [] a) { return Arrays.stream(a).collect(Collectors.toCollection(HashSet::new)); } public TreeSet TreeSet(T [] a) { return Arrays.stream(a).collect(Collectors.toCollection(TreeSet::new)); } public Deque Deque(T [] a) { return Arrays.stream(a).collect(Collectors.toCollection(ArrayDeque::new)); } public PriorityQueue PriorityQueue(T [] a) { return Arrays.stream(a).collect(Collectors.toCollection(PriorityQueue::new)); } // コレクション配列 public List [] ArrayList(int n) { @SuppressWarnings("unchecked") List [] G = new ArrayList[n]; for(int i = 0 ; i < n ; i ++ ) G[i] = new ArrayList<>(); return G ; } public HashSet [] HashSet(int n) { @SuppressWarnings("unchecked") HashSet [] G = new HashSet[n]; for(int i = 0 ; i < n ; i ++ ) G[i] = new HashSet<>() ; return G ; } public TreeSet [] TreeSet(int n) { @SuppressWarnings("unchecked") TreeSet [] G = new TreeSet[n]; for(int i = 0 ; i < n ; i ++ ) G[i] = new TreeSet<>() ; return G ; } public TreeSet [] TreeSet(int n , Comparator comparator) { @SuppressWarnings("unchecked") TreeSet [] G = new TreeSet[n]; for(int i = 0 ; i < n ; i ++ ) G[i] = new TreeSet<>(comparator) ; return G ; } public Deque [] Deque(int n) { @SuppressWarnings("unchecked") Deque [] G = new ArrayDeque[n]; for(int i = 0 ; i < n ; i ++ ) G[i] = new ArrayDeque<>(); return G ; } public PriorityQueue [] PriorityQueue(int n) { @SuppressWarnings("unchecked") PriorityQueue [] G = new PriorityQueue[n]; for(int i = 0 ; i < n ; i ++ ) G[i] = new PriorityQueue<>(); return G ; } public PriorityQueue [] PriorityQueue(int n , Comparator comparator) { @SuppressWarnings("unchecked") PriorityQueue [] G = new PriorityQueue[n]; for(int i = 0 ; i < n ; i ++ ) G[i] = new PriorityQueue<>(comparator); return G ; } public HashMap [] HashMap(int n) { @SuppressWarnings("unchecked") HashMap [] G = new HashMap[n]; for(int i = 0 ; i < n ; i ++ ) G[i] = new HashMap<>() ; return G ; } public TreeMap [] TreeMap(int n) { @SuppressWarnings("unchecked") TreeMap [] G = new TreeMap[n]; for(int i = 0 ; i < n ; i ++ ) G[i] = new TreeMap<>() ; return G ; } public TreeMap [] TreeMap(int n , Comparator comparator) { @SuppressWarnings("unchecked") TreeMap [] G = new TreeMap[n]; for(int i = 0 ; i < n ; i ++ ) G[i] = new TreeMap<>(comparator) ; return G ; } } final class FastScanner { private final InputStream in = System.in; private final Scanner sc = new Scanner(System.in); private final byte[] buffer = new byte[1024]; private int ptr = 0; private int buflen = 0; private boolean hasNextByte() { if (ptr < buflen) { return true; }else{ ptr = 0; try { buflen = in.read(buffer); } catch (IOException e) { e.printStackTrace(); } if (buflen <= 0) { return false; } } return true; } private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1; } private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126; } private boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) { ptr++; } return hasNextByte(); } public String next() { if (!hasNext()) throw new NoSuchElementException(); StringBuilder sb = new StringBuilder(); int b = readByte(); while(isPrintableChar(b)) { sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } public long nextLong() { if (!hasNext()) throw new NoSuchElementException(); long n = 0; boolean minus = false; int b = readByte(); if (b == '-') { minus = true; b = readByte(); } if (b < '0' || '9' < b) { throw new NumberFormatException(); } while(true){ if ('0' <= b && b <= '9') { n *= 10; n += b - '0'; }else if(b == -1 || !isPrintableChar(b)){ return minus ? -n : n; }else{ throw new NumberFormatException(); } b = readByte(); } } public int nextInt() { long nl = nextLong(); if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException(); return (int) nl; } public double nextDouble() { return Double.parseDouble(next()); } public char nextChar() { return next().charAt(0); } public BigInteger nextBigInteger() { return sc.nextBigInteger(); } public int [] nextInt(int n) { int [] array = new int[n]; for(int i = 0 ; i < n ; i ++) { array[i] = nextInt(); } return array ; } public int [][] nextInt(int n , int m) { int [][] array = new int[n][m]; for(int i = 0 ; i < n ; i ++) { array[i] = nextInt(m); } return array ; } public long [] nextLong(int n) { long [] array = new long[n]; for(int i = 0 ; i < n ; i ++) { array[i] = nextLong(); } return array ; } public long [][] nextLong(int n , int m) { long [][] array = new long[n][m]; for(int i = 0 ; i < n ; i ++) { array[i] = nextLong(m); } return array ; } public double [] nextDouble(int n) { double [] array = new double[n]; for(int i = 0 ; i < n ; i ++) { array[i] = nextDouble(); } return array ; } public String [] next(int n) { String [] array = new String[n]; for(int i = 0 ; i < n ; i ++) { array[i] = next(); } return array ; } public String [][] next(int n , int m) { String [][] array = new String[n][m]; for(int i = 0 ; i < n ; i ++) { array[i] = next(m); } return array ; } public char [] nextChar(int n) { return next().toCharArray(); } public char [][] nextChar(int n , int m) { char [][] array = new char[n][m]; for(int i = 0 ; i < n ; i ++) { array[i] = nextChar(m); } return array ; } }