Regex with Textbox with three kinds of letters and digits

HI ALL,
FIRST DIGIT IS BETWEEN 1-9 (I.E, 1,2,3,4,5,6,7,8,9). THE LENGTH WOULD BE ONLY 1 I.E., BETWEEN 1 AND 9.
MIDDLE DIGIT CAN START AND END WITH ANY NUMBERS BETWEEN 0-9 (99999,913234,93423432,023435,78945320 ETC....). NO LENGTH CONSTRAINT ON THIS.
LAST LETTER SHOULD BE "K" OR "M" (K OR M ONLY). THIS WOULD BE ONLY 1 LETTER EITHER K OR M
SO THE POSSIBLE COMBINATIONS WOULD BE 12343535K, 233435435M, 20293843K, 23353432M, 234M, 23535M, 23434K, 2M, 2K ANYTHING OF ABOVE SORT SHOULD BE ACCEPTED IN OUR TEXT BOX IN SILVERLIGHT APPLICATION. BUT THE EXPRESSSION IS SAME ACROSS WEBDEVELOPMENT I SUPPOSE
PLEASE LET ME IF YOU NEED ANYTHING ON THIS.
ANY HELP WOULD B ...