program ciur;
var A : array [1..2000000] of boolean;
    f : text;
    N,i,j,nr,i2,X : longint;
begin
assign(f,'ciur.in');
reset(f);
read(f,N);
close(f);
for i := 1 to N do
A[i] := true;
for i := 2 to n do
if A[i] then
  begin
    for j := 2 to n div i do A[i*j] := false;
    x:=x+1;
  end;
assign(f,'ciur.out');
rewrite(f);
write(f,X);
close(f);
end.