#include <iostream>
#include <vector>
#include <fstream>
using namespace std;
using ll = long long;

int n, k;
vector <ll> a(1e5 + 1, 0);
vector <ll> p(1e5 + 1, 0);
vector <ll> dp(1e5 + 1, 0);
vector <ll> cnt(1e5 + 1, -1);

ll sum(int l, int r) {
    return p[r] - p[l - 1];
}

pair <ll, ll> do_dp(ll lam) {
    dp[0] = -lam;
    int last = 0;
    for (int i = 1; i <= n; i++) {
        dp[i] = 1e18;
        for (int j = last; j < i; j++) {
            ll cur = dp[j] + lam + sum(j + 1, i) * (i - j);
            if (cur > dp[i]) break;
            dp[i] = cur;
            cnt[i] = cnt[j] + 1;
            last = j;
        }
    }
    return {cnt[n], dp[n]};
}

pair <ll, ll> do_dp2(ll lam) {
    dp[0] = -lam;
    int last = 0;
    for (int i = 1; i <= n; i++) {
        dp[i] = 1e18;
        for (int j = 0; j < i; j++) {
            ll cur = dp[j] + lam + sum(j + 1, i) * (i - j);
            if (cur<=dp[i]){
                dp[i]=cur;
                cnt[i]=cnt[j]+1;
            }
        }
    }
    return {cnt[n], dp[n]};
}

int main() {
    cin >> n >> k;
    for (int i = 1; i <= n; i++) {
        cin >> a[i];
        p[i] = p[i - 1] + a[i];
    }

    /*fstream fajl;
    fajl.open("be2.txt");
    fajl >> n >> k;
    for (int i = 1; i <= n; i++) {
        fajl >> a[i];
        p[i] = p[i - 1] + a[i];
    }
    fajl.close();*/

    ll l = 0, r = 1e18, m;
    while (r - l > 1) {
        m = (l + r) / 2;
        (do_dp2(m).first >= k ? l = m : r = m);
    }
    cout << do_dp2(l).second - k * l;
}