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
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knojbur
pmfm
 2
hk
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 5
zzxpfk
abcdefghijklmnopqrst
uvwxz
srgkjaskldfkln
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
tdxgc
lxyzgcmbzulcst
 5
dfijdfhi
abcdefghijklmnopqrst
uvwxy
kopsdfgiopjipw
jty
 2
xlaxwpjabtpwddc
txwdjmohrrszorrnomc
 1
a
 30
waiphwcqrrinr
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kjexeesevrlowxhghq
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etrjxdczppafly
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doxnxbjwptnimjmsuijx
zciwkbvrhgsjhrr
ehh
bzlnmd
xpbtbpftimnn
khbknqbvdkdd
mldj
skrvnyz
avptgpjmenfzfxwckmt
 30
e
x
itaubd
xcn
v
x
i
ci
aqs
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cvdu
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jos
qy
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nayke
ge
s
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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 l[29];
int main() {
  string x[100], z, w;
  int j, n, i, h = 0;
  scanf("%d", &n);
  for (i = 0; i < n; i++) cin >> x[i];
  for (i = 0; i < n; i++) {
    for (j = 0; j < x[i].size(); j++) {
      l[x[i][j] - 97] = 1;
    }
  }
  for (i = 0; i < 26; i++) {
    if (l[i] == 0) {
      z = 97 + i;
      break;
    } else
      h++;
  }
  if (h == 26) {
    z += "a";
    w = "a";
    for (i = 0; i < 26; i++) {
      w += "a";
      for (j = 0; j < n; j++) {
        if (w == x[j]) {
          w = "a";
          w += 97 + i + 1;
        } else {
          z = w;
          i = 25;
          break;
        }
      }
    }
  }
  cout << z;
  return 0;
}
