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

#include <bits/stdc++.h>
using namespace std;
int tree[13000][26];
char s[100];
queue<int> que;
queue<string> strque;
int main() {
  int num = 1, n, i, j, k;
  memset(tree, -1, sizeof(tree));
  scanf("%d", &n);
  for (i = 0; i < n; i++) {
    scanf("%s", s);
    for (j = 0; s[j]; j++) {
      int cur = 0;
      for (k = j; s[k]; k++) {
        int idx = s[k] - 'a';
        if (tree[cur][idx] == -1) {
          tree[cur][idx] = num++;
        }
        cur = tree[cur][idx];
      }
    }
  }
  que.push(0);
  strque.push(string(""));
  while (que.empty() == false) {
    int tmp = que.front();
    que.pop();
    string str = strque.front();
    strque.pop();
    for (i = 0; i < 26; i++) {
      if (tree[tmp][i] == -1) {
        cout << str + char('a' + i);
        return 0;
      }
      que.push(tree[tmp][i]);
      strque.push(str + char('a' + i));
    }
  }
  return 0;
}
