program ciur;
var v:array[2..2000000] of boolean;
    i,j,nr:word;
    n:longint;
    f,g:text;
begin
    assign(f,'ciur.in');
    assign(g,'ciur.out');
    reset(f);
    rewrite(g);
    read(f,n);
    nr:=0;
    fillchar(v,sizeof(v),true);
    for i:=2 to trunc(sqrt(n)) do
        if v[i] then
        begin
            j:=2;
            while(i*j<=n) do
            begin
                v[i*j]:=false;
                inc(j);
            end;
        end;
    for i:=2 to n do
        if v[i] then inc(nr);
    write(g,nr);
    close(f);
    close(g);
end.