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

using LL = long long;

int main() {
    ios_base::sync_with_stdio(false);
    
    int n, k;
    cin >> n >> k;
    vector<LL> a(n);
    for (LL &x : a) cin >> x;
    auto check = [&](LL s) {
        LL sum = 0, w;
        int cnt = 0;
        for (int i = 0; i < n; i++) {
            if (a[i] + sum < s) {
                w = (s - a[i] - sum + i) / (i + 1);
                if (cnt + w > k) return false;
                sum += w * (i + 1), cnt += w;
            }
        }
        return true;
    };

    LL l, r, mid, res;
    l = 0, r = 1E18;
    while (l <= r) {
        mid = l + r >> 1;
        if (check(mid)) {
            l = (res = mid) + 1;
        } else {
            r = mid - 1;
        }
    }
    cout << res;

    return 0;
}