function zero(n:longint):longint;
var f,r:longint;
begin
  r:=0; f:=5;
  while (n>=f) do begin r:=r+n div f; f:=f*5; end;
  zero:=r;
end;

var p,k,n:longint;

begin
  assign(input,'fact.in'); reset(input);
  assign(output,'fact.out'); rewrite(output);
  readln(p); k:=4*p; n:=k-k mod 5;
  repeat
    k:=zero(n);
    if k<p then inc(n,5);
  until k>=p;
  if k>p then n:=-1
  else if p=0 then n:=1;
  writeln(n);
  close(input); close(output);
end.