var nr,z,p,n,i:integer;
		f:text;
begin
  assign(f,'fact.in');reset(f);
	read(f,p);
  assign(f,'fact.out');rewrite(f);
  z:=0;i:=1;
  while z < p do
  	begin
      nr := i;
      while nr mod 5 = 0 do
    	  begin
      	  inc(z);
          nr := nr div 5;
        end;
      inc(i);
    end;
  if z>p then
  	writeln(f,-1)
  else
	  writeln(f,i-1);
  close(f);
end.