{
TASK:rprimes
LANG:PASCAL
}
program primes;
var a,b,i,h,j,n:longint;
    s:integer;
    x:boolean;
begin
 readln(a,b);
 s:=0;
 for i:=a to b do begin
  x:=true;
   n:=i div 2;
  for j:=2 to n do
   if (i mod j=0) then begin
    x:=false;
    break;
   end;
  if x then begin
   h:=i;
   while ((h div 10>0) and x ) do begin
    h:=h div 10;
    n:=h div 2;
    for j:=2 to n do
     if (h mod j=0) then begin
      x:=false;
      break;
     end;
   end;
  end;
  if (x and (h<>1)) then s:=s+1;
 end;
writeln(s);
end.