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
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o
a
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 5
splt
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 2
hk
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 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
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qiqehzmgsjdoqd
kjexeesevrlowxhghq
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z
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szahigtmklglrcocbo
znligfxkgxzkcfeu
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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
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nayke
ge
s
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qwad
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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 n;
string s[40];
bool check[30];
bool check1[680];
int main() {
  if (0) {
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
  };
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) cin >> s[i];
  for (int i = 1; i <= n; i++)
    for (int j = 0; j < s[i].length(); j++) check[int(s[i][j] - 'a')] = true;
  for (int i = 0; i < 26; i++)
    if (!check[i]) {
      cout << char(i + 'a');
      return 0;
    }
  for (int i = 1; i <= n; i++)
    for (int j = 0; j < s[i].length() - 1; j++)
      check1[(s[i][j] - 'a') * 26 + (s[i][j + 1] - 'a')] = true;
  for (char i = 'a'; i <= 'z'; i++)
    for (char j = 'a'; j <= 'z'; j++)
      if (!check1[(i - 'a') * 26 + (j - 'a')]) {
        cout << i << j;
        return 0;
      }
  return 0;
}
