#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <tuple>
#include <cmath>
#include <numeric>
#include <functional>
#include <cassert>

#define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl;
#define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

using namespace std;
typedef long long ll;

template<typename T>
vector<vector<T>> vec2d(int n, int m, T v){
    return vector<vector<T>>(n, vector<T>(m, v));
}

template<typename T>
vector<vector<vector<T>>> vec3d(int n, int m, int k, T v){
    return vector<vector<vector<T>>>(n, vector<vector<T>>(m, vector<T>(k, v)));
}

template<typename T>
void print_vector(vector<T> v, char delimiter=' '){
    if(v.empty()) {
        cout << endl;
        return;
    }
    for(int i = 0; i+1 < v.size(); i++) cout << v[i] << delimiter;
    cout << v.back() << endl;
}


// calc ceil(a/b) 
template<typename T>
T ceil_div(T a, T b){
    return (a+b-1)/b;
}


const ll inf = 1e18;

void solve(){
    int n, k; cin >> n >> k;
    vector<ll> a(n);
    for(int i = 0; i < n; i++) cin >> a[i];
    auto ok = [&](ll x){
        ll cnt = 0;
        ll sum = 0;
        for(int i = 0; i < n; i++){
            ll cur = a[i]+sum;
            if(x <= cur) continue;
            ll c = ceil_div(x-cur, (ll)i+1);
            cnt += c;
            if(cnt > k) return false;
            sum += ((ll)(i+1))*c;
        }
        return cnt <= k;
    };
    ll l = 0, r = inf;
    while(r-l > 1){
        ll x = (l+r)/2;
        if(ok(x)) l = x;
        else r = x;
    }
    cout << l << endl;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    solve();
}