#include <bits/stdc++.h>
#include <atcoder/all>
#define OVERLOAD_REP(_1, _2, _3, name, ...) name
#define REP1(i,n) for (auto i = std::decay_t<decltype(n)>{}; (i) != (n); ++(i))
#define REP2(i,l,r) for (auto i = (l); (i) != (r); ++(i))
#define rep(...) OVERLOAD_REP(__VA_ARGS__, REP2, REP1)(__VA_ARGS__)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
using namespace std;
using namespace atcoder;
using ll = long long;
using ull = unsigned long long;
using P = pair<int,int>;
using LP = pair<long long,long long>;
using SP = pair<string,string>;
using vi = vector<int>;
using vl = vector<long long>;
using vs = vector<string>;
using vc = vector<char>;
using mint1 = modint1000000007;
using mint9 = modint998244353;
const int INF = 2e9;
const long long LINF = 4e18;
const int di[] = {0,1,0,-1,-1,1,-1,1};
const int dj[] = {1,0,-1,0,1,1,-1,-1};
template<class T> inline bool chmin(T& a, T b){if(a>b){a=b;return true;}return false;}
template<class T> inline bool chmax(T& a, T b){if(a<b){a=b;return true;}return false;}
void YesNo (bool ok , const string &s , const string &t) {if(ok) cout << s << endl; else cout << t << endl;} 


//-----def end-----//

int main () {
    long long n , k;
    cin >> n >> k;
    vector<long long> a(n);
    rep(i , n) cin >> a[i];
    long long l = -1 , r = 1e16;
    auto f = [&] (long long m) {
        long long sum = 0 , cnt = 0;
        rep(i , n) {
            if(a[i]+sum >= m) continue;
            long long op = (m-(a[i]+sum)+i)/(i+1);
            cnt += op;
            sum += op*(i+1);
        }
        return cnt;
    };
    while (r-l>1) {
        long long mid = (l+r)/2;
        if(f(mid) <= k) l = mid;
        else r = mid;
    }
    cout << l << endl;
	return 0;
}