#include <bits/stdc++.h>
#define int long long
using namespace std;
typedef array<int, 2> pr;
const int MAX = 300001;
const int INF = 90'000'000'000;
const int REAL_INF = 0x3f3f3f3f3f3f3f3f;
int A[MAX], S[MAX];
pr dp[MAX][2];
pr max(pr X, pr Y) { return X[0] == Y[0] ? (X[1] > Y[1] ? X : Y) : (X[0] > Y[0] ? X : Y); }
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(0), cout.tie(0);
int N, K, ans, st, en, md;
pr V;
cin >> N >> K;
for (int i = 1; i <= N; i++)
cin >> A[i], S[i] = S[i - 1] + A[i];
ans = REAL_INF;
dp[0][1] = {-INF, 0};
st = -INF, en = INF;
while (st <= en) {
md = st + en >> 1;
for (int i = 1; i <= N; i++) {
dp[i][0] = max(dp[i - 1][0], dp[i - 1][1]);
dp[i][1] = max({dp[i - 1][0][0] + A[i] - md, dp[i - 1][0][1] + 1}, {dp[i - 1][1][0] + A[i], dp[i - 1][1][1]});
}
V = max(dp[N][0], dp[N][1]), ans = min(ans, V[0] + md * K);
if (V[1] <= K)
en = md - 1;
else
st = md + 1;
}
cout << max(0ll, ans) << '\n';
return 0;
}
