# 最低値の目標まで何回で到達できるか、二分探索、でどうか

N, K = map(int, input().split())
A = list(map(int, input().split()))

#X = 5
from math import ceil

def check(X):
    count = 0
    added = 0
    for i in range(N):
        num = A[i]
        if num + added < X:
            subcount = ceil((X-num-added)/(i+1))
            count += subcount
            added += (i+1)*subcount
    #print(count)
    if count <= K:
        return 1
    else: 
        return 0
    
#for x in range(20):
#    print(x, check(x))

OK = 0
NG = 10**20
while NG-OK>1:
    mid = (OK+NG)//2
    if check(mid) == 1:
        OK = mid
    else:
        NG = mid
print(OK)