from sys import stdin input=lambda :stdin.readline()[:-1] n,k=map(int,input().split()) a=list(map(int,input().split())) def calc(mid): c=0 num=0 for i in range(n): if a[i]+num<mid: use=(mid-a[i]-num+i)//(i+1) c+=use num+=(i+1)*use return c<=k ng,ok=10**15,-1 while abs(ng-ok)>1: mid=(ng+ok)//2 if calc(mid): ok=mid else: ng=mid print(ok)