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
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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 argc, char *argv[]) {
  int n;
  cin >> n;
  vector<string> s(n);
  set<char> one;
  set<string> two;
  string tmp = "  ";
  for (int i = 0; i < n; ++i) {
    cin >> s[i];
    int size = s[i].size();
    one.insert(s[i][0]);
    for (int j = 1; j < size; ++j) {
      one.insert(s[i][j]);
      tmp[0] = s[i][j - 1];
      tmp[1] = s[i][j];
      two.insert(tmp);
    }
  }
  if (one.size() < 26) {
    for (char c = 'a'; c <= 'z'; ++c) {
      if (one.count(c) == 0) {
        cout << c << endl;
        break;
      }
    }
  } else {
    string c = "  ";
    bool found = false;
    for (char c1 = 'a'; !found && c1 <= 'z'; ++c1) {
      c[0] = c1;
      for (char c2 = 'a'; !found && c2 <= 'z'; ++c2) {
        c[1] = c2;
        if (two.count(c) == 0) {
          cout << c << endl;
          found = true;
        }
      }
    }
  }
  return EXIT_SUCCESS;
}
