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
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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
gtpr
kuzoxmiixxbl
crgqtuo
jhbplhpklrgwnaugdf
zuxdaat
aycv
qwghrkqwkobrgevsjrk
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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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
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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 a, c, d[205], f, n, b, x, i;
string s, s1, s11, s12;
char i1, i2, j;
int main() {
  cin >> n;
  for (i = 1; i <= n; i++) {
    cin >> s1;
    b = s1.size();
    c = c + b;
    s = s + '%';
    s = s + s1;
  }
  c = c + n - 1;
  for (i1 = 'a'; i1 <= 'z'; i1++) {
    s1 = i1;
    x = s.find(s1);
    if (x == -1) {
      cout << s1;
      return 0;
    }
  }
  for (i1 = 'a'; i1 <= 'z'; i1++) {
    for (i2 = 'a'; i2 <= 'z'; i2++) {
      s11 = i1;
      s12 = i2;
      s1 = s11 + s12;
      x = s.find(s1);
      if (x == -1) {
        cout << s1;
        return 0;
      }
    }
  }
}
