What was the gas consumption peak month for SME customers in 2013?
'in 2013' refers to the first 4 strings of yearmonth.date = '2013', The 5th and 6th string of the date can refer to month.
SELECT SUBSTRING(T2.Date, 5, 2) FROM customers AS T1 INNER JOIN yearmonth AS T2 ON T1.CustomerID = T2.CustomerID WHERE SUBSTRING(T2.Date, 1, 4) = '2013' AND T1.Segment = 'SME' GROUP BY SUBSTRING(T2.Date, 5, 2) ORDER BY SUM(T2.Consumption) DESC LIMIT 1