program factorial;
var n,p,i,j,i1:longint;
    f,g:text;
begin
assign(f,'fact.in');
reset(f);
read(f,p);
close(f);
assign(g,'fact.out');
rewrite(g);
j:=0;i:=0;
if p=0 then
  j:=1
else
  begin
  repeat
  i:=i+1;
    begin
    i1:=i;
    while (i1 mod 5=0) and (j<p) do
      begin
      j:=j+1;
      i1:=i1 div 5;
      end;
    end;
  until j=p;
  end;
write(g,j);
close(g);
end.