#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef unsigned long long int ull;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll myRand(ll B) { return (ull)rng() % B; }

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n, k;
    cin >> n >> k;
    vector<ll> r_sum(n + 1);
    vector<ll> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
        r_sum[i + 1] = r_sum[i] + a[i];
    }
    ll L = 0, R = 1e18;

    auto solve = [&](ll x) -> bool {
        int cnt = 0;
        ll sum = 0;
        for (int i = 0; i < n; i++) {
            sum += a[i];
            if (sum >= x) {
                sum = 0;
                cnt++;
            }
        }
        if (cnt <= k - 2) return false;
        if (cnt >= k) return true;
        vector<int> left(n, -1);
        sum = 0;
        int r = 0;
        for (int l = 0; l < n; l++) {
            while (r < n and sum < x) {
                sum += a[r];
                r++;
            }
            if (sum >= x) {
                left[l] = r;
            } else break;
            sum -= a[l];
        }
        vector<pair<int, int>> v(n + 1);
        for (int i = 0; i <= n; i++) {
            v[i] = {0, i};
        }
        for (int i = n - 1; i >= 0; i--) {
            if (left[i] == -1) continue;
            int nxt = left[i];
            v[i] = v[nxt];
            v[i].first++;
        }

        ll pre_sum = 0;
        ll suf_sum = 0;
        for (int i = 0; i < n; i++) {
            if (v[i].first != k - 1) break;
            int ed = v[i].second;
            // [ed,n)
            suf_sum = r_sum[n] - r_sum[ed];
            if (pre_sum + suf_sum >= x) return true;
            pre_sum += a[i];
        }
        return false;
    };

    while (R - L > 1) {
        ll mid = (L + R) / 2;
        if (solve(mid)) {
            L = mid;
        } else {
            R = mid;
        }
    }

    cout << L << endl;
}