Program eratosthenes;
var
i,n,j,x,k:longint;
prim:boolean;
cin,cout:text;
begin
assign(cin,'ciur.in');reset(cin);
assign(cout,'ciur.out');rewrite(cout);
read(cin,n);
k:=0;
x:=2;
for i:=2 to n do
  begin
  prim:=true;
  for j:=2 to (x div 2) do
    begin
    if (x mod j=0) then
      prim:=false;
    end;
  if (prim=true) then
    k:=k+1;
  x:=x+1;
  end;
writeln(cout,k);
close(cin);
close(cout);
end.