def dectobap(pi):
    bap=[]
    tau = list(pi)
    for j in range(0,len(tau)):
        if tau[j]==(j+1):
            #pos.dec., need to have j+n
            bap.append(j+1+len(tau))
        elif tau[j]<0:
            #neg.dec., need to have j
            bap.append(j+1)
        else:
            #displaced points, need to have been j and j+n
            if tau[j]<(j+1):
                add_n=tau[j]+len(tau)
                bap.append(add_n)
            else:
                bap.append(tau[j])
    return bap

def statistic(pi):
    step=0
    tau = dectobap(pi)
    for i in range(0,len(tau)-1):  #stops at 2nd to last index
          if abs(tau[i+1]-tau[i])>step:
                step=abs(tau[i+1]-tau[i])
    return step