program setb;
var a,b,p,i,j,n,t:longword;
  s:array[1..10000]of longword;
  w:array[1..100000]of boolean;
  ok:boolean;
function su(k:longword):boolean;
var i:integer;
begin
  if k=2 then exit(true);
  for i:=2 to trunc(sqrt(k)) do if k mod i = 0 then exit(false);
  exit(true);
end;
begin
  assign(input,'setb.in'); reset(input);
  assign(output,'setb.out'); rewrite(output);
  fillchar(w,sizeof(w),false); n:=0;
  readln(a,b,p);
  for i:=a to b do w[i]:=true;
  for i:=p to b do if su(i) then begin inc(n); s[n]:=i; end;
  t:=0;
  for i:=n downto 1 do
  begin
    ok:=false; j:=a;
    if j mod s[i]<>0 then j:=(a div s[i])*s[i]+s[i];
    repeat
      if (j<=b)and(w[j])and(j mod s[i]=0)
        then begin
          w[j]:=false;
          ok:=true;
        end;
      inc(j,s[i]);
    until j>=b;
    if ok then inc(t);
  end;
  writeln(t);
  close(input); close(output);
end.