v=strsplit(readLines('stdin'),'')[[1]]\x0d
d=length(v)\x0d
h=d/2+0.5\x0d
m=matrix(' ',d,d)\x0d
diag(m)=m[h,]=m[,h]=diag(m[d:1,])=v\x0d
invisible(cat((apply(m,2,paste,collapse='')),sep='\n'))
Note that non-ascii characters in the above source code will be escaped (such as \x9f).