Table:
text: 1957–58 Segunda División
Group II
Group II
Position_ Club Played Points Wins Draws Losses Goals_for Goals_against Goal_Difference
1 Real Betis 34 42 18 6 10 66 42 +24
2 CD Tenerife 34 38 15 8 11 61 40 +21
3 Real Murcia 34 38 15 8 11 54 42 +12
4 Levante UD 34 37 15 7 12 65 48 +17
5 Hércules CF 34 36 15 6 13 57 54 +3
6 CD San Fernando 34 36 14 8 12 51 45 +6
7 AD Plus Ultra 34 36 13 10 11 55 53 +2
8 CD Eldense 34 35 14 7 13 57 68 -11

Question: What is the lowest goal difference of club Real Betis who has less than 18 wins in Segunda División Group II 1957–58?