3
rjnflsbpxqivrcdjptj
vpojopbwbwbswdu
rydkiwnugwddcgcrng
 1
z
 30
b
u
p
n
f
m
t
i
j
k
p
h
a
c
w
z
z
p
t
d
o
w
u
q
l
y
i
o
a
u
 5
splt
ohqykk
xqpz
knojbur
pmfm
 2
hk
obsp
 5
zzxpfk
abcdefghijklmnopqrst
uvwxz
srgkjaskldfkln
vgnsdfdgfh
 2
rxscdzkkezud
wjehahqgouqvjienq
 5
ojdfhi
abcdefghijklmnopqrst
uvwxyz
ddfhdfhlasjt
qqq
 1
epkotfpkkrhhmuipmtdk
 10
kpmwcdoysw
gtpr
kuzoxmiixxbl
crgqtuo
jhbplhpklrgwnaugdf
zuxdaat
aycv
qwghrkqwkobrgevsjrk
tdxgc
lxyzgcmbzulcst
 5
dfijdfhi
abcdefghijklmnopqrst
uvwxy
kopsdfgiopjipw
jty
 2
xlaxwpjabtpwddc
txwdjmohrrszorrnomc
 1
a
 30
waiphwcqrrinr
o
qiqehzmgsjdoqd
kjexeesevrlowxhghq
judikhzkj
z
xo
lsdzypkfqro
sshgcxsky
gecntpcmoojfwp
svmytmcfhc
jrsrvsvbaiumlmkptn
s
wpcsovfjlyspviflk
ktvyzvddgllht
szahigtmklglrcocbo
znligfxkgxzkcfeu
liryvzmqwhr
xgrxkgiehxztv
etrjxdczppafly
jrdgajschhwsci
doxnxbjwptnimjmsuijx
zciwkbvrhgsjhrr
ehh
bzlnmd
xpbtbpftimnn
khbknqbvdkdd
mldj
skrvnyz
avptgpjmenfzfxwckmt
 30
e
x
itaubd
xcn
v
x
i
ci
aqs
zbi
q
cvdu
a
jos
qy
fjf
nayke
ge
s
q
qwad
gvz
o
ubn
nzoc
h
wnjwjrf
t
bq
bw
 1
b

a
 a
 e
 a
 a
 y
 b
 aa
 a
 ab
 z
 e
 b
 aa
 l
 a

import java.util.*;

public class B {
	static final int LETTERS = 'z' - 'a' + 1;
	static class Trie{
		Trie [] nodes = new Trie[LETTERS];
		Trie(){
			
		}
	}
	static final Comparator<String> CMP = new Comparator<String>(){
		public int compare(String s1, String s2){
			int cmp = s1.length() - s2.length();
			if (cmp == 0){
				cmp = s1.compareTo(s2);
			}
			return cmp;
		}
	};
	static String rec(String current, Trie node){
		for (int i = 0; i < LETTERS; ++i){
			if (node.nodes[i] == null){
				return current + (char)('a' + i);
			}
		}
		String res = null;
		for (int i = 0; i < LETTERS; ++i){
			if (node.nodes[i] != null){
				String next = rec(current + (char)('a' + i), node.nodes[i]);
				if (res == null || CMP.compare(res, next) > 0){
					res = next;
				}
			}
		}
		return res;
	}
	public static void main(String [] args){
		try (Scanner s = new Scanner(System.in)){
			Trie trie = new Trie();
			for (int n = Integer.parseInt(s.nextLine()); n > 0; --n){
				final String text = s.nextLine();
				for(int i = 0; i < text.length(); ++i){
					for (int j = i; j < text.length(); ++j){
						Trie currentNode = trie;
						for (int k = i; k <= j; ++k){
							if (currentNode.nodes[text.charAt(k) - 'a'] == null){
								currentNode = currentNode.nodes[text.charAt(k) - 'a'] = new Trie();
							}else{
								currentNode = currentNode.nodes[text.charAt(k) - 'a'];
							}	
						}
					}
				}
			}
			System.out.println(rec("", trie));
		}
	}
}
