[igraph] How to find node name(id)

[shahab]

Hi,
I have rather stupid problem, which I don't how to solve.
After invoking any of Closeness, Betweeness, Pagerank , etc, I want to
get the node name corresponding node name(id) for some computed score
(lets's say top scores).
The loaded graph is "edge list" format.
I use the following script ,  could you please point me to the place
that I can get the node name:

library(igraph)
g<-read.graph("network.txt", format="edgelist",0, TRUE)
btw<-betweenness(g)
top_btw<-head(sort(btw, decr = T))
cat("  Top Scores:", top_btw, "\n")

cat("   Nodes with Top scores:",?????????????)

best,
/Shahab