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
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 5
zzxpfk
abcdefghijklmnopqrst
uvwxz
srgkjaskldfkln
vgnsdfdgfh
 2
rxscdzkkezud
wjehahqgouqvjienq
 5
ojdfhi
abcdefghijklmnopqrst
uvwxyz
ddfhdfhlasjt
qqq
 1
epkotfpkkrhhmuipmtdk
 10
kpmwcdoysw
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kuzoxmiixxbl
crgqtuo
jhbplhpklrgwnaugdf
zuxdaat
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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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znligfxkgxzkcfeu
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doxnxbjwptnimjmsuijx
zciwkbvrhgsjhrr
ehh
bzlnmd
xpbtbpftimnn
khbknqbvdkdd
mldj
skrvnyz
avptgpjmenfzfxwckmt
 30
e
x
itaubd
xcn
v
x
i
ci
aqs
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q
cvdu
a
jos
qy
fjf
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 main() {
  int N;
  cin >> N;
  string all_words[N];
  for (int i = 0; i < N; i++) {
    cin >> all_words[i];
  }
  string ans = "a";
  bool flag = false;
  while (!flag) {
    for (int i = 0; i < 26; i++) {
      flag = true;
      ans[ans.length() - 1] = i + 'a';
      for (int j = 0; j < N; j++) {
        string check = all_words[j];
        for (int k = 0; k < check.length(); k++) {
          if (check.substr(k, ans.length()) == ans) {
            flag = false;
          }
        }
      }
      if (flag) {
        cout << ans << endl;
        flag = true;
        break;
      }
    }
    ans[ans.length() - 1] = 'a';
    ans = ans + "a";
  }
}
