N,K=map(int,input().split())
A=list(map(int,input().split()))
L,R=0,10**18
while L<R:
  M=(L+R+1)>>1
  C=0
  D=0
  for i in range(N):
    V=(M-(A[i]+C)+i)//(i+1)
    if V>0:
      C+=V*(i+1)
      D+=V
  if D<=K:
    L=M
  else:
    R=min(R-1,M)
print(L)