program factorial;

var w:int64;
    e,o:integer;

procedure citire;
begin
assign(input,'fact.in');
reset(input);
read(w);
close(input);
end;

function zero(x:int64):integer;
var p:integer;
begin
p:=0;
while x mod 10=0 do
      begin
      inc(p);
      x:=x div 10;
      end;
zero:=p;
end;

procedure scriere;
begin
assign(output,'fact.out');
rewrite(output);
write(o);
close(output);
end;

procedure prelucrare;
var q:int64;
    i:integer;
begin
q:=1;
o:=-1;
if w=0 then
   o:=1
   else begin
        //for i:=2 to  do
        i:=2;
        while true do
              begin
              q:=q*i;
              if q<0 then
                 break;
              if q mod 10=0 then
                 begin
                 e:=zero(q);
                 if e=w then
                    begin
                    o:=i;
                    break;
                    end;
                 end;
              inc(i);
              end
        end
end;

begin
citire;
prelucrare;
scriere;
end.