program project1;
var A, B, q, M, k, Mmin, kp, l: uint64;
    f0, f1: text;
begin
     assign(f0, 'input.txt');
     reset(f0);
     read(f0, A, B, q);
     close(f0);
     assign(f1, 'output.txt');
     rewrite(f1);
     k:=2;
     Mmin:=high(uint64);
     while k <= q div k do
           Begin
           If q mod k = 0 then
              Begin
              l:=0;
              While (q mod k = 0) do
                  Begin
                  inc(l);
                  q:=q div k;
                  End;
              M:=0;
              kp:=k;
              while kp <= B do
                    Begin
                    M:=M + ((B div kp) - ((A - 1) div kp));
                    if kp <= high(uint64) div k then
                       kp:=kp*k else break;
                    End;
              M:=M div l;
              if M < Mmin then Mmin:=M;
              end;
           Inc(k);
           End;
      If q > 1 then
         Begin
         kp:=q;
         M:=0;
         while kp <= B do
            Begin
            M:=M + ((B div kp) - ((A - 1) div kp));
            if kp <= (high(uint64) div q) then
               kp:=kp*q else break;
            End;
         if M < Mmin then Mmin:=M;
         end;
      write(f1, Mmin);
      close(f1);
end.