#include <iostream>
#include <vector>
#include <atcoder/all>

#define ALL(V) std::begin(V), std::end(V)

using ll = long long;

ll ceil_div(ll a, ll b) {
    return a / b + !!(a % b);
}

int main() {
    ll N, K;
    std::cin >> N >> K;
    std::vector<ll> A(N);
    for (auto &e : A) std::cin >> e;

    ll ok = 0, ng = 1e16;
    while (1 < std::abs(ok - ng)) {
        ll mid = (ok + ng) / 2;
        ll sum = 0, cnt = 0;
        for (ll i = 1; i <= N; i++) {
            ll e = A[i - 1];
            if (mid <= e + sum) continue;
            ll use = ceil_div(mid - (e + sum), i);
            sum += use * i;
            cnt += use;
        }
        (cnt <= K ? ok : ng) = mid;
    }
    std::cout << ok << std::endl;
    return 0;
}