program ciurul_lui_Eratostene;
var v1,v2:array[2..2000000] of longint;
    nr,i,j,prime:longint;
    f:text;
begin
prime:=0;
assign(f,'ciur.in');
reset(f);
readln(f,nr);
close(f);
for i:=2 to nr do
  v1[i]:=i;
for i:=2 to nr do
  begin
    if(v2[i]=0) then
      begin
        for j:=2 to nr do
          begin
            v2[i*j]:=1;
          end;
      end;
  end;
 for i:=2 to nr do
   begin
    if(v2[i]=0) then prime:=prime+1;
   end;
 assign(f,'ciur.out');
 rewrite(f);
 writeln(f,prime);
 close(f);
end.