const
  m=26;
var
  a,b,c:integer;
  i:array[1..m-1]of integer;
  n:array[0..m-1]of integer;
  s,p,o:string;
begin
  {coder}
  a:=7;
  b:=5;
  for c:=0 to m-1 do n[c]:=(a*c+b)mod m;
  s:='example of encryption and decryption by the affine Caesar permutation system';
  write('Enter string:=',s);
{  readln(s);}
  while pos(' ',s)>0 do delete(s,pos(' ',s),1);
  s:=UpperCase(s);
  o:=s;
  for c:=1 to length(s)do
{    if s[c] in ['A'..'Z']then }s[c]:=chr(ord('A')+n[ord(s[c])-ord('A')]);
  writeln('Code   string:=',s);
  readln;
  {decoder}
  for c:=1 to m-1 do i[c]:=0;
  for c:=1 to m-1 do for b:=1 to m-1 do
      if(b<>c)and((b*c mod m)=1)then i[c]:=b;
  for a:=0 to m-1 do
    begin
{      writeln('':15,s);}
      for c:=1 to m-1 do if i[c]<>0 then
        begin
          p:=s;
          write('Decode string:=');
          for b:=0 to m-1 do n[b]:=i[c]*(m+b-a)mod m;
          for b:=1 to length(p)do
{            if p[b] in ['A'..'Z']then }p[b]:=chr(ord('A')+n[ord(p[b])-ord('A')]);
{          if p=o then writeln(p,' bingo')else} writeln(p);
        end;
      readln;
    end;
end.