function nr5(a:longint):word;
var i:integer;
begin
  i:=0;
  while a mod 5=0 do begin inc(i);a:=a div 5; end;
  nr5:=i;
end;

var p,n,nr0:longint;
begin
assign(input,'fact.in');reset(input);
assign(output,'fact.out');rewrite(output);
  readln(p);
  if p=0 then n:=1 else begin
    n:=0;nr0:=0;
    while nr0<>p do begin inc(n,5);nr0:=nr0+nr5(n);end;
    write(n);
  end;
close(input);close(output);
end.