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
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y
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o
a
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 5
splt
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 2
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 5
zzxpfk
abcdefghijklmnopqrst
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vgnsdfdgfh
 2
rxscdzkkezud
wjehahqgouqvjienq
 5
ojdfhi
abcdefghijklmnopqrst
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ddfhdfhlasjt
qqq
 1
epkotfpkkrhhmuipmtdk
 10
kpmwcdoysw
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kuzoxmiixxbl
crgqtuo
jhbplhpklrgwnaugdf
zuxdaat
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qwghrkqwkobrgevsjrk
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lxyzgcmbzulcst
 5
dfijdfhi
abcdefghijklmnopqrst
uvwxy
kopsdfgiopjipw
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 2
xlaxwpjabtpwddc
txwdjmohrrszorrnomc
 1
a
 30
waiphwcqrrinr
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kjexeesevrlowxhghq
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doxnxbjwptnimjmsuijx
zciwkbvrhgsjhrr
ehh
bzlnmd
xpbtbpftimnn
khbknqbvdkdd
mldj
skrvnyz
avptgpjmenfzfxwckmt
 30
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itaubd
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x
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ci
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jos
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ge
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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 glob = 1;
int main() {
  int t, i, j, temp;
  string a[30], test("a"), test2, sum, temp2;
  sum.clear();
  char ch[10];
  cin >> t;
  for (i = 0; i < t; i++) {
    cin >> a[i];
    sum.append(" ");
    sum.append(a[i]);
  }
  while (1) {
    if (sum.find(test) != std::string::npos) {
      glob++;
      temp = glob;
      test2.clear();
      for (i = 0; temp != 0; i++) {
        if (temp % 27 == 0) {
          temp++;
          continue;
        }
        ch[0] = 'a' + temp % 27 - 1;
        ch[1] = '\0';
        temp2.clear();
        temp2.assign(ch);
        test2.append(string(temp2));
        temp = temp / 27;
      }
      i = 0;
      test.clear();
      for (std::string::reverse_iterator rit = test2.rbegin();
           rit != test2.rend(); ++rit) {
        ch[0] = *rit;
        ch[1] = '\0';
        temp2.clear();
        temp2.assign(ch);
        test.append(string(temp2));
      }
    } else
      break;
  }
  cout << test;
  return 0;
}
