Program xuat_hien;
Uses crt;
Var

        S: string; i,so:integer; ch: char;
        dem: array['a'..'z'] of integer;
Begin
      Clrscr;
        Write('Nhap xâu S: '); Readln(S);
        For ch:='a' to 'z' do
        Dem[ch]:=0;so:=0;
        For i:=1 to length(S) do Inc(dem[S[i]]);
        For ch:='a' to 'z' do
        If dem[ch]=2 then inc(so);
        write(so);
        Readln;
End.

*Em chạy CT xem được chưa nha

#HNgoc

#Chuc_em_hoc_tot

uses crt;
var i,dem:longint; s:string; c:char; f:array['a'..'z']of longint;
begin 
clrscr;
   write('Nhap xau S: ');readln(s);
   for i:=1 to length(s) do inc(f[s[i]]);
   for c:='a' to 'z' do 
      if f[c]=2 then inc(dem);
   writeln(dem);
readln
end.