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
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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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lxyzgcmbzulcst
 5
dfijdfhi
abcdefghijklmnopqrst
uvwxy
kopsdfgiopjipw
jty
 2
xlaxwpjabtpwddc
txwdjmohrrszorrnomc
 1
a
 30
waiphwcqrrinr
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kjexeesevrlowxhghq
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z
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szahigtmklglrcocbo
znligfxkgxzkcfeu
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etrjxdczppafly
jrdgajschhwsci
doxnxbjwptnimjmsuijx
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ehh
bzlnmd
xpbtbpftimnn
khbknqbvdkdd
mldj
skrvnyz
avptgpjmenfzfxwckmt
 30
e
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itaubd
xcn
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x
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ci
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jos
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ge
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ubn
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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;
set<string> ttls;
void addTitle(const string& str) {
  for (int i = 0; i < str.size(); i++) {
    for (int j = 1; j <= str.size() - i; j++) {
      string s = str.substr(i, j);
      ttls.insert(s);
    }
  }
}
int main() {
  int n = 0;
  cin >> n;
  for (__typeof(n) i = 0; i < n; i++) {
    string str;
    cin >> str;
    addTitle(str);
  }
  int curLen = 1;
  char curStr[33];
  curStr[0] = 'a';
  while (true) {
    string sss(curStr, curLen);
    cout << ":::::" << sss << endl;
    if (ttls.find(sss) == ttls.end()) {
      cout << sss;
      break;
    }
    bool isZllZ = true;
    for (__typeof(curLen) i = 0; i < curLen; i++) {
      if (curStr[i] != 'z') {
        isZllZ = false;
        break;
      }
    }
    if (isZllZ) {
      curLen++;
      for (__typeof(curLen) i = 0; i < curLen; i++) curStr[i] = 'a';
    } else {
      int nzi = curLen - 1;
      while (curStr[nzi] == 'z') nzi--;
      curStr[nzi]++;
      nzi++;
      while (nzi < curLen) {
        curStr[nzi] = 'a';
        nzi++;
      }
    }
  }
}
