program setb(input,output);
const
 su:array[1..168]of integer=(2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,101,103,107,109,
113,127,131,137,139,149,151,157,163,167,173,179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271,277,
281,283,293,307,311,313,317,331,337,347,349,353,359,367,373,379,383,389,397,401,409,419,421,431,433,439,443,449,457,461,
463,467,479,487,491,499,503,509,521,523,541,547,557,563,569,571,577,587,593,599,601,607,613,617,619,631,641,643,647,653,
659,661,673,677,683,691,701,709,719,727,733,739,743,751,757,761,769,773,787,797,809,811,821,823,827,829,839,853,857,859,
863,877,881,883,887,907,911,919,929,937,941,947,953,967,971,977,983,991,997);
var
 a,b:longint;
 i,j:longint;
 p,ans:longint;
 z:Array[1..100000]of longint;
 s:array[1..100000]of boolean;

procedure count;
var
 i:longint;
begin
 for i:=a to b do
  if s[i]=true then
  begin
   s[i]:=false;
   inc(ans);
  end;
end;

function max(a,b:longint):longint;
begin
 if a>b then max:=b else max:=a;
end;

function ju(k,l:longint):longint;
var
 g,o,q:longint;
begin
 ju:=1;
 for g:=1 to 168 do
  if su[g]>=p then
  begin
   o:=g;
   break;
  end;
 for g:=1 to 168 do
  if (su[g]<max(k,l))and(su[g+1]>max(k,l)) then
  begin
   q:=g+1;
   break;
  end;
 for g:=o to q do
  if (k mod su[g]=0)and(l mod su[g]=0) then
  begin
   ju:=su[g];
   exit;
  end;
end;

begin
 assign(input,'setb.in');
 reset(input);
 readln(a,b,p);
 if a>b then
 begin
  i:=a;
  a:=b;
  b:=i;
 end;
 for i:=a to b do
  z[i]:=i;
 close(input);

 for i:=a to b do
  for j:=a to b do
   if z[i]<>z[j] then
   begin
    if ju(i,j)>=p then z[j]:=z[i];
   end;

 for i:=a to b do s[z[i]]:=true;
 count;

 assign(output,'setb.out');
 rewrite(output);
 writeln(ans);
 close(output);
end.