var p:longint;
		f:text;
function func(nr:longint):longint;
var n,r,i:longint;
begin
  r:=0;
	for i := 1 to nr do
    begin
    	n:=i;
      while n mod 5 = 0 do
      	begin
        	inc(r);
          n := n div 5;
        end;
    end;
  func:=r;
end;
procedure bin(a,b:longint);
var r,c:longint;
begin
  if a>b then
    write(f,-1)
  else
    begin
    c:=(a+b) div 2;
    r:=func(c);
    if r<p then
  	  bin(c+1,b)
    else if r>p then
  	  bin(a,c-1)
    else if r=p then
  	  write(f,c-(c mod 5));
  end;
end;
begin
  assign(f,'fact.in');reset(f);
	read(f,p);
  assign(f,'fact.out');rewrite(f);
  if p=0 then
  	write(f,1)
  else
	  bin(0,p*5);
  close(f);
end.