program fainnaspa;
var v:array[1..2000010]of boolean;
    f,g:text;
    i,n,c,j:int64;
begin
assign(f,'ciur.in');reset(f);
assign(g,'ciur.out');rewrite(g);
read(f,n);
fillchar(v,sizeof(v),false);
i:=3;c:=1;
while i<=n do begin
      if not v[i] then begin
         j:=i*i;c:=c+1;
         while j<=n do begin
               v[j]:=true;
               j:=j+i;
         end;end;
       i:=i+2;
end;
writeln(g,c);
close(f);close(g);
end.