Remove NAs from Barplot

Dear List:

I'm creating a series of barplots using Sweave that must assume a
standard format. This is student achievement data and the x-axis must
include all grades 3 to 8. In some cases, the data for a grade (or more
than one grade) are missing in the vector math.bar, but are never
missing for the vector apmxpmeet. The following sample code illustrates
the issue.

Using the code below to create the plot works fine. However, the
following command is designed to place the data onto the plot:

text(math.barplot, graph.max+5, format(tot), xpd = TRUE, col = c("blue",
"orange") )

This does work, but, it also places 'NA's on the plot. Is there a way to
place the data onto the plot such that the numbers appear, but for the
NAs not to appear?  I've searched through ?text but was not able to find
a solution. 

math.bar <- c(NA,NA,NA,NA,55,48)
apmxpmeet <- c(47, 50, 49, 50, 49, 46)

par(ps=10)
math.bar <- rbind(math.bar, apmxpmeet)
math.barplot <- barplot(math.bar, beside=T, col=c('blue','orange'),
names=c('Grade \n 3','Grade \n 4','Grade \n 5','Grade \n 6','Grade \n
7','Grade \n 8'), 
ylim=c(0,120), ylab="Percentage", xlab="Grade Level")
tot <- round(math.bar,digits=0)
graph.max <- max(math.bar, apmxpmeet, na.rm=T)
text(math.barplot, graph.max+5, format(tot), xpd = TRUE, col = c("blue",
"orange") )
tmp$sch_nameS05 <- as.character(tmp$sch_nameS05)
legend(2,120,legend=(c(tmp$sch_nameS05, "Average")),
fill=c("blue","orange"))

Thanks,
Harold

format(tot)

tot

tmp$sch_nameS05 <- as.character(tmp$sch_nameS05)