program fact;
var f,g:text;
    c5,c2,i,aux,c:longint;
    p:longint;
begin
  assign(f,'fact.in');
  reset(f);
  assign(g,'fact.out');
  rewrite(g);
  readln(f,p);
  if p=0 then
    writeln(g,'1')
  else
  begin
  i:=0;
  while p<>c do
    begin
      i:=i+1;
      if i mod 2=0 then
       begin
        aux:=i;
        while aux mod 2=0 do
          begin
           c2:=c2+1;
           aux:=aux div 2;
          end;
       end;
      if i mod 5=0 then
        begin
          aux:=i;
          while aux mod 5=0 do
            begin
              c5:=c5+1;
              aux:=aux div 5;
            end;
        end;
      if c2<c5 then
        c:=c2
      else
        c:=c5;
    end;
  writeln(g,i);
  end;
  close(f);
  close(g);
end.