Combining dates

Hello,
i have 116 thoudsands of lines of data and they have seperated it by year, day month and i need to get them combined and some of them are just the date here is an example from my excel 2007 i need them to have the forward slash and the full year has to be there
thanks
michele
1533 1
1533 2
1541 4
1543
1552 2 7
1553
1555 15 11
1557 2
1562 28 10
1566
1567 3
1568
1568
1568 4 4
1568
1570 8 2
1574
1574
1575 17 3
1575 16 12
1576 7
1577
1578 17 6
1581
1581
1582 22 1
1582 7 8
1582 15 8
1584
1584 17 3
1584
1586 10 7
1587 4 9
1590
1590
1590 4
1592
1592
1594
st the year i have microsoft excel 2007