program nr_zerouri_la_factorial;
var n,p,c:integer;
    f,h:text;
function nr5(m:integer):integer;
var b:integer;
begin
  b:=0;
  while (m mod 5 = 0) do
    begin
     b:=b+1; m:=m div 5;
    end;
   nr5:=b;
 end; {nr5}

begin
  assign(f,'fact.in'); reset(f);
  readln(f,p);  close(f);
  n:=1; c:=0;
  while (c<p) do
    begin
      inc(n); while (n mod 5 <> 0) do inc(n);
      c:=c+nr5(n);
    end;
    
     assign(h,'fact.out'); rewrite(h); writeln(h,n); close(h);

end.