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
s
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 n;
  cin >> n;
  string arr[n];
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
  }
  string vars[26] = {"a", "b", "c", "d", "e", "f", "g", "h", "i",
                     "j", "k", "l", "m", "n", "o", "p", "q", "r",
                     "s", "t", "u", "v", "w", "x", "y", "z"};
  set<string> uniq;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < arr[i].length(); j++) {
      uniq.insert(vars[arr[i][j] - 97]);
      if (j < arr[i].length() - 1)
        uniq.insert(vars[arr[i][j] - 97] + vars[arr[i][j + 1] - 97]);
    }
  }
  for (int i = 0; i < 26; i++) {
    string x = vars[i];
    if (uniq.find(x) == uniq.end()) {
      cout << x << "\n";
      return 0;
    }
  }
  for (int i = 0; i < 26; i++) {
    for (int j = 0; j < 26; j++) {
      string x = vars[i] + vars[j];
      if (uniq.find(x) == uniq.end()) {
        cout << x << "\n";
        return 0;
      }
    }
  }
}
