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 main() {
  int n;
  char ch[30];
  bool exist1[26] = {false}, exist2[26][26] = {false};
  scanf("%d", &n);
  for (int i = 0; i < n; ++i) {
    scanf("%s", ch);
    for (int j = 0; j < strlen(ch); ++j) {
      exist1[ch[j] - 'a'] = true;
    }
    for (int j = 1; j < strlen(ch); ++j) {
      exist2[ch[j - 1] - 'a'][ch[j] - 'a'] = true;
    }
  }
  bool found = false;
  for (char c = 'a'; c <= 'z'; ++c) {
    if (!exist1[c - 'a']) {
      printf("%c\n", c);
      found = true;
      break;
    }
  }
  if (!found) {
    for (char c1 = 'a'; !found && c1 <= 'z'; ++c1) {
      for (char c2 = 'a'; c2 <= 'z'; ++c2) {
        if (!exist2[c1 - 'a'][c2 - 'a']) {
          printf("%c%c\n", c1, c2);
          found = true;
          break;
        }
      }
    }
  }
  return 0;
}
