program setb(input,output);

var
  i,j,k,a,b,p,st,en:longint;
  pp:array[0..10000]of longint;
  num:array[1..1000000]of longint;
  boo:array[1..2000000]of boolean;

procedure makeprime;
  var
    i:integer;
    boo:boolean;
  begin
    pp[0]:=1;
    pp[1]:=2;
    i:=3;
    repeat
      boo:=true;

      for j:=2 to trunc(sqrt(i)) do
        if i mod j=0 then
        begin
          boo:=false;
          break;
        end;

      if boo then
      begin
        inc(pp[0]);
        pp[pp[0]]:=i;

        if (i>=p)and(st=0) then
          st:=pp[0];

        if i>b then
        begin
          en:=pp[0]-1;
          exit;
        end;
      end;

      inc(i,2);
    until 0=1;
  end;

begin
  assign(input,'setb.in');
  reset(input);
  assign(output,'setb.out');
  rewrite(output);

  readln(a,b,p);
  makeprime;

  for i:=a to b do
    num[i]:=i;

  for i:=st to en do
    for j:=a to b do
      if j mod pp[i]=0 then
      begin
        if num[j]<>j then
          for k:=a to b do
            if (num[j]=num[k])and(k<>j) then
              num[k]:=1000000+i;
        num[j]:=1000000+i;
      end;

  st:=0;
  for i:=a to b do
    if not(boo[num[i]]) then
    begin
      boo[num[i]]:=true;
      inc(st);
    end;

  writeln(st);

  close(input);
  close(output);
end.