#include <bits/stdc++.h>
#ifndef LOCAL_TEST
#pragma GCC target ("avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#endif // LOCAL_TEST
using namespace std;
using ll = long long;
using pii = pair<int, int>; using pll = pair<ll, ll>;
using vi = vector<int>;  using vvi = vector<vi>; using vvvi = vector<vvi>;
using vl = vector<ll>;  using vvl = vector<vl>; using vvvl = vector<vvl>;
using vb = vector<bool>; using vvb = vector<vb>; using vvvb = vector<vvb>;
using vc = vector<char>; using vvc = vector<vc>; using vvvc = vector<vvc>;
using vd = vector<double>; using vvd = vector<vd>; using vvvd = vector<vvd>;
using vs = vector<string>; using vvs = vector<vector<string>>; using vvvs = vector<vector<vector<string>>>;
template <class T> using priority_queue_min = priority_queue<T, vector<T>, greater<T>>;
constexpr double PI = 3.14159265358979323;
constexpr int INF = 100100111; constexpr ll INFL = 3300300300300300491LL;
float EPS = 1e-8; double EPSL = 1e-16;
bool eq(const double x, const double y) { return abs(x - y) < EPSL; }
bool eq(const float x, const float y) { return abs(x - y) < EPS; }
template<typename T> bool eq(const T x, const T y) { return x == y; }
template<typename T> bool neq(const T x, const T y) { return !(eq(x, y)); }
template<typename T> bool ge(const T x, const T y) { return eq(x, y) || (x > y); }
template<typename T> bool le(const T x, const T y) { return eq(x, y) || (x < y); }
template<typename T> bool gt(const T x, const T y) { return !(le(x, y)); }
template<typename T> bool lt(const T x, const T y) { return !(ge(x, y)); }
constexpr int MODINT998244353 = 998244353;
constexpr int MODINT1000000007 = 1000000007;
struct Nyan { Nyan() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(18); } } nyan;
#define all(a) (a).begin(), (a).end()
#define sz(x) ((int)(x).size())
#define rep(i, n) for(ll i = 0, i##_len = ll(n); i < i##_len; ++i) // 0 から n-1 まで昇順
#define repi(i, s, t) for(ll i = ll(s), i##_end = ll(t); i < i##_end; ++i) // s から t まで昇順
#define repis(i, s, t, step) for(ll i = ll(s), i##_end = ll(t); i < i##_end; i+=step) // s から t まで stepずつ
#define repir(i, s, t, step) for(ll i = ll(s), i##_end = ll(t); i > i##_end; i+=step) // s から t まで stepずつ
#define repe(a, v) for(auto& a : (v)) // v の全要素（変更可能）
#define smod(n, m) ((((n) % (m)) + (m)) % (m)) // 非負mod
#define sdiv(n, m) (((n) - smod(n, m)) / (m)) // 非負div
void Yes(bool b) { cout << (b ? "Yes\n" : "No\n"); return; }
void YES(bool b) { cout << (b ? "YES\n" : "NO\n"); return; }

ll powm(ll a, ll n, ll mod=INFL) {
    ll res = 1;
    while (n > 0) {
        if (n & 1) res = (res * a) % mod;
        if (n > 1) a = (a * a) % mod;
        n >>= 1;
    }
    return res;
}
ll sqrtll(ll x) {
    assert(x >= 0);
    ll hi(x), lo(0);
    while (hi != lo) {
        ll y = (hi + lo + 1) / 2;
        if (y <= x/y) lo = y;
        else hi = y - 1;
    }
    return lo;
}
template <class T> inline bool chmax(T& M, const T& x) { if (M < x) { M = x; return true; } return false; } // 最大値を更新（更新されたら true を返す）
template <class T> inline bool chmin(T& m, const T& x) { if (m > x) { m = x; return true; } return false; } // 最小値を更新（更新されたら true を返す）
int digit(ll x, int d=10) { int rev=0; while (x > 0) { rev++; x /= d;}; return rev; } // xのd進数桁数
#include <functional>
template <class T, class F> T binsearch(T s, T e, F le) {
    T cmin = s;
    T cmax = e;
    while (cmin != cmax) {
        T p = (cmin + cmax + 1) / 2;
        if (le(p)) cmin = p;
        else cmax = p - 1;
    }
    return cmin;
}
template <class F> double binsearch_double(double s, double e, F le, double eps=1e-10) {
    double cmin = s;
    double cmax = e;
    while (abs(cmax - cmin) > eps) {
        double p = (cmin + cmax) / 2;
        if (le(p)) cmin = p;
        else cmax = p;
    }
    return cmin;
}
template <class T, class F> T ternary_search(T s, T e, F f, double eps=1e-10) {
    T cmin = s;
    T cmax = e;
    while (cmax - cmin > (T)3) {
        T p1 = cmin + max<T>(1, (cmax - cmin) / 3);
        T p2 = cmax - max<T>(1, (cmax - cmin) / 3);
        if (f(p1) > f(p2)) cmin = p1;
        else cmax = p2;
    }
    T rev = cmin;
    auto val = f(cmin);
    rep(i, 4) {
        if (chmin<T>(val, f(cmin+i))) rev = cmin + i;
    }
    return rev;
}
template <class F> double ternary_search_double(double s, double e, F f, double eps=1e-10) {
    double cmin = s;
    double  cmax = e;
    while (abs(cmax - cmin) > eps) {
        double p1 = cmin + (cmax - cmin) / 3;
        double p2 = cmax - (cmax - cmin) / 3;
        if (f(p1) > f(p2)) cmin = p1;
        else cmax = p2;
    }
    return cmin;
}
template <class T, class U> inline istream& operator>>(istream& is, pair<T, U>& p);
template <class T> inline istream& operator>>(istream& is, vector<T>& v);
template <class T, class U> inline ostream& operator<<(ostream& os, const pair<T, U>& p);
template <class T> inline ostream& operator<<(ostream& os, const vector<T>& v);
template <typename T, typename S> ostream &operator<<(ostream &os, const map<T, S> &mp);
template <typename T> ostream &operator<<(ostream &os, const set<T> &st);
template <typename T> ostream &operator<<(ostream &os, const multiset<T> &st);
template <typename T> ostream &operator<<(ostream &os, queue<T> q);
template <typename T> ostream &operator<<(ostream &os, deque<T> q);
template <typename T> ostream &operator<<(ostream &os, stack<T> st);
template <class T, class Container, class Compare> ostream &operator<<(ostream &os, priority_queue<T, Container, Compare> pq);

template <class T, class U> inline istream& operator>>(istream& is, pair<T, U>& p) { is >> p.first >> p.second; return is; }
template <class T> inline istream& operator>>(istream& is, vector<T>& v) { repe(x, v) is >> x; return is; }
template <class T, class U> inline ostream& operator<<(ostream& os, const pair<T, U>& p) { os << p.first << " " << p.second; return os; }
template <class T> inline ostream& operator<<(ostream& os, const vector<T>& v) { rep(i, sz(v)) { os << v.at(i); if (i != sz(v) - 1) os << " "; } return os; }
template <typename T, typename S> ostream &operator<<(ostream &os, const map<T, S> &mp) { for (auto &[key, val] : mp) { os << key << ":" << val << " "; } return os; }
template <typename T> ostream &operator<<(ostream &os, const set<T> &st) { auto itr = st.begin(); for (int i = 0; i < (int)st.size(); i++) { os << *itr << (i + 1 != (int)st.size() ? " " : ""); itr++; } return os; }
template <typename T> ostream &operator<<(ostream &os, const multiset<T> &st) { auto itr = st.begin(); for (int i = 0; i < (int)st.size(); i++) { os << *itr << (i + 1 != (int)st.size() ? " " : ""); itr++; } return os; }
template <typename T> ostream &operator<<(ostream &os, queue<T> q) { while (q.size()) { os << q.front() << " "; q.pop(); } return os; }
template <typename T> ostream &operator<<(ostream &os, deque<T> q) { while (q.size()) { os << q.front() << " "; q.pop_front(); } return os; }
template <typename T> ostream &operator<<(ostream &os, stack<T> st) { while (st.size()) { os << st.top() << " "; st.pop(); } return os; }
template <class T, class Container, class Compare> ostream &operator<<(ostream &os, priority_queue<T, Container, Compare> pq) { while (pq.size()) { os << pq.top() << " "; pq.pop(); } return os; }
template <class T> inline vector<T>& operator--(vector<T>& v) { repe(x, v) --x; return v; }
template <class T> inline vector<T>& operator++(vector<T>& v) { repe(x, v) ++x; return v; }

#define debug(...) debug_func(0, #__VA_ARGS__, __VA_ARGS__) // debug print
#ifdef LOCAL_TEST
template <typename T>
void debug_func(int i, T name) { (void)i; (void)name; cerr << endl; }
template <typename T1, typename T2, typename... T3> void debug_func(int i, const T1 &name, const T2 &a, const T3 &...b) {
  for ( ; name[i] != ',' && name[i] != '\0'; i++ ) cerr << name[i];
  cerr << ":" << a << " ";
  debug_func(i + 1, name, b...);
}
#endif
#ifndef LOCAL_TEST
template <typename... T>
void debug_func(const T &...) {}
#endif

int main() {
    ll  n,k;
    cin >> n >> k;
    vl a(n);
    cin >> a;
    auto lt = [&] (ll x) -> bool {
        ll add = 0;
        ll num = 0;
        rep(i, n) {
            if (a[i] + add < x) {
                ll numc = (x - a[i] - add - 1) / (i+1) + 1;
                if (numc > k) return false;
                num += numc;
                add += numc * (i + 1);
            }
        }
        return num <= k;
    };
    cout << binsearch(0LL, powm(10, 16), lt) << endl;
}