#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    ll n, k, INF = 1ll << 61;
    cin >> n >> k;
    vector<ll> a(n);
    for(auto &&v:a)cin >> v;
    ll ok = 0, ng = 1ll << 60, mid;
    while(ok + 1 < ng){
        mid = (ok + ng) / 2;
        ll cnt = 0, s = 0;
        for(int i = 0; i < n; i++){
            if(a[i] + s < mid){
                ll d = i + 1, di = mid - (a[i] + s);
                cnt = min(INF, cnt + (di + d - 1) / d);
                s = min(INF, s + (di + d - 1) / d * d);
            }
        }
        if(cnt <= k) ok = mid;
        else ng = mid;
    }
    cout << ok << '\n';
}