n <- 100
support <- 1:n
walk <- cumsum(2*rbinom(n,1,0.5)-1)
graph <- function(k) {
  plot(1:k, walk[support<=k], xlim=c(1,n), ylim=c(-n/10,n/10), type="l")
  Sys.sleep(0.1)
}
ignore <- sapply(support, graph)