var f,g:text;
    a:array[1..2000000]of 0..1;
    n,b:longint;
function ciur(x:longint):longint;
var i,y,nr:longint;
begin
nr:=0;
for i:=2 to n do
    if a[i]=0 then begin y:=i;
                        while y<=n do
                        begin
                          y:=y+i;
                          a[y]:=1;
                        end;
                      nr:=nr+1;
                    end;
ciur:=nr;
end;
begin
assign(f,'ciur.in'); assign(g,'ciur.out'); reset(f); rewrite(g);
read(f,n);
b:=ciur(n);
write(g,b);
close(f); close(g);
end.