import sys
input = sys.stdin.readline

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

def judge(x):
    k=K
    s=0
    for i,a in enumerate(A,start=1):
        if a+s>=x:continue
        d = x-(a+s)
        p=(d+i-1)//i
        k-=p
        if k<0:return False
        s+=i*p
    return True

ok,ng=0,10**15
while ok+1<ng:
    m=ok+ng>>1
    if judge(m):
        ok=m
    else:
        ng=m
print(ok)