uses crt,math;
type int = longint;
var a,b,s1,s2:string;
    l,i,m,j:int;
begin
    clrscr;
    readln(a);
    readln(b);
    l:=length(a);
    m:=min(l,length(b));
    s1:=a[l];
    s2:=b[1];
    dec(l);i:=2;
    for j:=m downto 1 do
        begin
            if s1 <> s2 then
                begin
                    s1:=a[l] + s1;
                    s2:=s2 + b[i];
                    dec(l);inc(i);
                end
            else
                break;
        end;
    if s1 <> s2 then writeln('khong co')
    else writeln(s1);
readln;
end.

var x,y,s,s1,s2:ansistring;
  i,j,n:longint;
begin
 readln(x);
 read(y); 
for i := 1 to length(x) do
 if pos(x[i],s1) = 0 then
   s1 := s1 + x[i];
for j := 1 to length(y) do
 if pos(y[j],s2) = 0 then
   s2 := s2 + y[j];
for i := 1 to length(s1) do
 for j := 1 to length(s2) do
   if s1[i] = s2[j] then
     s := s+s1[i];
writeln(s);
readln; readln;
end.