program bai_giai;
uses crt;
var x:string;
i,j,d,max:byte;
c:char;
begin
clrscr;
readln(x);
max:=1;
for i:=1 to length(x)-1 do
begin
d:=1;
for j:=i+1 to length(x) do
if x[i]=x[j] then d:=d+1;
if d>max then
begin
max:=d; c:=x[i];
end;
end;
write(c);
readln;
end.