/* -*- coding: utf-8 -*-
 *
 * 2217.cc:  No.2217 Suffix+ - yukicoder
 */

#include<cstdio>
#include<algorithm>
 
using namespace std;

/* constant */

const int MAX_N = 100000;

/* typedef */

typedef long long ll;

/* global variables */

ll as[MAX_N];

/* subroutines */

ll check(int n, ll x) {
  ll c = 0, s = 0;
  for (int i = 0; i < n; i++)
    if (x > as[i] + s) {
      ll d = (x - (as[i] + s) + i) / (i + 1);
      c += d;
      s += d * (i + 1);
    }
  return c;
}

/* main */

int main() {
  int n, k;
  scanf("%d%d", &n, &k);
  for (int i = 0; i < n; i++) scanf("%lld", as + i);

  ll x0 = 0, x1 = 200000000000000LL + 1;
  while (x0 + 1 < x1) {
    ll x = (x0 + x1) / 2;
    if (check(n, x) > k) x1 = x;
    else x0 = x;
  }

  printf("%lld\n", x0);
  return 0;
}