import sys
input = sys.stdin.readline

def judge(x):
    add = 0
    need = 0
    
    for i in range(N):
        lack = max(0, x-A[i]-add)
        c = (lack+i)//(i+1)
        need += c
        add += c*(i+1)
    
    return need<=K

N, K = map(int, input().split())
A = list(map(int, input().split()))
ok = -1
ng = 10**18

while abs(ok-ng)>1:
    mid = (ok+ng)//2
    
    if judge(mid):
        ok = mid
    else:
        ng = mid

print(ok)