Monweek2week


 * monweek to week
 * YYYY-Www → YYYY-MM-Ww
 * ISO-8601
 * test set
 * 2012-01-W1 → 2012-W01
 * 2012-03-W3 → 2012-W11
 * 2012-12-W4 → 2012-W52

1 cell
=TEXT(DATE(LEFT(A1,4),MID(A1,6,2),4)+7*(RIGHT(A1,1)-1),"YYYY")&"-W"&TEXT(INT((DATE(LEFT(A1,4),MID(A1,6,2),4)+7*(RIGHT(A1,1)-1)-DATE(YEAR(DATE(LEFT(A1,4),MID(A1,6,2),4)+7*(RIGHT(A1,1)-1)-WEEKDAY(DATE(LEFT(A1,4),MID(A1,6,2),4)+7*(RIGHT(A1,1)-1)-1)+4),1,3)+WEEKDAY(DATE(YEAR(DATE(LEFT(A1,4),MID(A1,6,2),4)+7*(RIGHT(A1,1)-1)-WEEKDAY(DATE(LEFT(A1,4),MID(A1,6,2),4)+7*(RIGHT(A1,1)-1)-1)+4),1,3))+5)/7),"00")

2 cells

 * B1
 * =DATE(LEFT(A1,4),MID(A1,6,2),4)+7*(RIGHT(A1,1)-1)


 * C1
 * =TEXT(B1,"YYYY")&"-W"&TEXT(INT((B1-DATE(YEAR(B1-WEEKDAY(B1-1)+4),1,3)+WEEKDAY(DATE(YEAR(B1-WEEKDAY(B1-1)+4),1,3))+5)/7),"00")