var n,i,nr,j:longint;
    prim:array[1..2000000] of 0..1;
    f,g:text;
begin
assign(f,'ciur.in');
assign(g,'ciur.out');
reset(f);
rewrite(g);
readln(f,n);
nr:=1; i:=3;
while i<=n do
begin
if prim[i]=0 then
        begin
        nr:=nr+1;
        j:=i+i;

        while j<=n do
                begin
                prim[j]:=1;
                J:=j+i;
                end;
        end;
        I:=i+2;
end;
writeln(g,nr);
close(f);
close(g);
end.