const f='ciur.in';g='ciur.out';
    nmax=2000001;
var
    v:array[1..nmax] of char;
    n,i,j,cate:integer;
begin
    assign(input,f);reset(input);
    assign(output,g);rewrite(output);
    read(n);
    for i:=2 to n do   v[i]:='1';
    for i:=2 to n do
        if v[i]='1' then
            begin
            inc(cate);
            j:=i+i;
            while j<=n do
                begin
                v[j]:='0';
                j:=j+i;
                end;
            end;
    write(cate);
    close(input);close(output);
end.