var a:array[1..2000000] of boolean;
    f:text;
    i,j,n,db:longint;
begin
        assign(f,'ciur.in'); reset(f);
        readln(f,n);
        a[1]:=false;
        for i:=2 to n do a[i]:=true;
        db:=0;
        for i:=2 to n do
                if a[i] then begin inc(db);
                                   for j:=2 to n div i do a[i*j]:=false;
                             end;
        assign(f,'ciur.out'); rewrite(f);
        writeln(f,db);
        close(f);
end.