program ciureratostene;
var a:array[1..64000] of boolean;
    f,g:text;
    n,i,j,nr:longint;
begin
         assign(f,'ciur.in');
         reset(f);
         read(f,n);
         close(f);

         for i:=1 to n do
          a[i]:=true;

    for i:=2 to n do
       if a[i]=true then
       for j:=2 to n div i do
             a[i*j]:=false;
                       nr:=0;
          for i:=2 to n do
           if a[i]=true then nr:=nr+1;

        assign(g,'ciur.out');
        rewrite(g);
        write(g,nr);
        close(g);
end.