An unbiased coin is tossed 12 times.The probability that at least 7 consecutive heads show up is  $\frac{K}{256}$  then   K=

The sequence of consecutive heads may starts with 1^st toss or 2^nd toss or 3^rd toss ---- or at 6^th toss. In any case, if it starts with r th throw, the first (r-2) throws may be head or tail but  (r-1)st throw must be  tail, after which again a head or tail can show up: