uses crt;
var f:text; s:string; i:longint;
begin
clrscr;
write('S=');readln(s);
for i:=1 to length(s) do
while not((s[i] in ['a'..'z'])or(s[i] in ['0'..'9'])or(s[i]=' ')) do
delete(s,i,1);
assign(f,'dulieu.txt');rewrite(f);
writeln(f,'Xau sau khi xu li: ',s);
close(f);
readln
end.