var a:array[1..2000000] of boolean;
    i,n,k,c:integer;
    f,g:text;
begin
assign(f,'ciur.in');
reset(f);
readln(f,n);
close(f);
for i:=2 to n do
    a[i]:=true;
c:=0;
for i:=2 to n do
    begin
    if a[i] then
                begin
                k:=i+i;
                c:=c+1;
                        while k<=n do
                                begin
                                a[k]:=false;
                                k:=k+1;
                                end;
                 end;
    end;
assign(g,'ciur.out');
rewrite(g);
writeln(g,c);
close(g);
end.