function (K,n,a) 
{
N<-K*n; sale<-rep(0,K)
sale[sample(1:K,1)]<-1
for(i in 2:N){
  p<-(1-a)/K+a*sale/(i-1)
  k<-sample(1:K,1,prob=p)
  sale[k]<-sale[k]+1
  }
sale
}