program cat4;

    var

      a,b, q, d, g, p,z, min, l: qword;
    begin
      Assign(input, 'input.txt'); reset(input);
      Assign(output, 'output.txt');rewrite(output);
      Read(a,b,q);

      d := 2;
      p := q;
      min := high(qword);
      z := 0;


      while (d <= q div d) do
      begin
        if (q mod d = 0) then
        begin

          l := 0;
          g := d;
          z := 0;

          while (q mod d = 0) do
          begin
            l:=l+1;
            q := q div d;
          end;

          while (b div g > 0) do
          begin
            z := z + (b div g) - ((a - 1) div g);
            if (g <= high(qword) div d) then
              g := d * g else break;
          end;

          z := z div l;
          if z < min then min := z;
        end;

        d:=d+1;

      end;

      if (q > 1) then
      begin

      p := q;
      z := 0;

        while (b div q > 0) do
        begin
          z := z + (b div q) - ((a - 1) div q);
          if (p <= high(qword) div q) then
            q := q * p else break;
        end;

        if z < min then   min := z;

      end;

      write( min);
      Close(output);
    end.