program alex;
var f:text;
    i,k,n,j:longint;
    p:array[1..20000]of 0..1;
begin
assign(f,'ciur.in'); reset(f);
read(f,n);
close(f);
for i:=1 to n do
    p[i]:=1;
i:=2;
k:=0;
while i<=n do
      begin
      if p[i]=1 then begin
                     k:=k+1;
                     j:=i+i;
                     while j<=n do
                           begin
                           p[j]:=0;
                           j:=j+i;
                           end;
                     end;
     i:=i+1;
     end;
assign(f,'ciur.out');rewrite(f);
write(f,k);
close(f);
end.