#include <bits/stdc++.h> 
#include <atcoder/all>
#define pub push_back
#define eb emplace_back
#define mp make_pair
#define fi first
#define se second
#define rep(i, n) rep2(i, 0, n)
#define rep2(i, m, n) for (ll i = m; i < (n); i++)
#define per(i, b) per2(i, 0, b)
#define per2(i, a, b) for (ll i = int(b) - 1; i >= int(a); i--)
#define ALL(c) (c).begin(), (c).end()
using namespace std;
using namespace atcoder;
using ll = long long;
using Pll = pair<ll, ll>;
using mint = modint998244353;
using mint2 = modint1000000007;

constexpr long long INF = (1LL << 60);
constexpr double EPS = 1e-9;
constexpr double PI = 3.141592653589;

template <typename T>
bool chmax(T& a, const T& b) {
    if (a < b) {
        a = b;  // aをbで更新
        return true;
    }
    return false;
}

template <typename T>
bool chmin(T& a, const T& b) {
    if (a > b) {
        a = b;  // aをbで更新
        return true;
    }
    return false;
}

template <typename T>
T sq(T x) {
    return x * x;
}

std::string zfill(int n, const int width)
{
    std::stringstream ss;
    ss << std::setw(width) << std::setfill('0') << n;
    return ss.str();
}



int main(void) {
    //cout << fixed << setprecision(10);
    ll N, K; cin >> N >> K;
    vector<ll> A(N);
    rep(i, N) {
        cin >> A[i];
    }
    ll high = (ll)1e18;
    ll low = 0;
    while (high > low) {
        ll mid = (high + low) / 2;
        ll now = 0;
        ll sousa = 0;
        rep(i, N) {
            if (mid > A[i] + now) {
                ll p = (mid - A[i] - now) / (i + 1);
                if ((mid - A[i] - now) % (i + 1) != 0) {
                    p++;
                }
                sousa += p;
                now += (i + 1) * p;
            }
        }
        if (sousa > K) {
            high = mid;
        }
        else {
            low = mid;
        }
        if (high == low + 1) {
            break;
        }
    }
    cout << low << endl;
}