Cash flow statement - CONFIRMATION OF STATEMENT

Cash flow is calculated by making certain adjustments to net income by adding or subtracting differences in revenue, expenses, and credit transactions (appearing on the balance sheet and income statement) resulting from transactions that occur from one period to the next. So period ending june is to be taken. 

If your doing monthly, it should be May because working capital changes is between current period and previous period.

What ever it is, comparison can be done between only one period, so use may.