var n,i,j,nr:longint;
    v:array[1..2000001] of byte;
f,g:text;
begin
assign(f,'ciur.in');
reset(f);
assign(g,'ciur.out');
rewrite(g);
readln(f,n);
nr:=0;
for i:=2 to trunc(sqrt(n)) do
       if v[i]=0 then begin
       for j:=2 to (n div i) do
           v[i*j]:=1;
           end;
for i:=2 to n do
if v[i]=0 then nr:=nr+1;
writeln(g,nr);
close(f);
close(g);
end.