p <- 18/38
q <- 1-p
n <- 100
c <- 50
m <- matrix(0, n+1, n+1)
for (i in 2:n) {
  m[i,i-1] <- q
  m[i,i+1] <- p
}

# Absorbing barriers on both sides:
m[1,1] <- 1
m[n+1,n+1] <- 1

x <- matrix(0, 1, n+1)
x[1,c+1] <- 1
for (i in 1:2000) {
  x <- x %*% m
  plot((1:(n+1))[x>0], x[x>0], xlim=c(1,n+1), 
       ylim=c(0,1), xlab="n", ylab="P(X=n)")
}