Подсчитать количество шипящих букв в слове- QBasic(Бейсик)

data "ж","ш","ч","щ"
dim a$(4)
for i=1 to 4
read a$(i)
next
input b$
for i=1 to len(b$)
for j=1 to 4
if mid$(b$,i,1)=a(j)then k=k+1
next
next
print k