// 赤コーダーになりたい
// お願い いいですか？
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
// Pragmas
// #pragma GCC optimize("Ofast")
// #pragma GCC optimize("unroll-loops")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
// Namespaces
using namespace std;
using namespace __gnu_pbds;
// Data types
using si = short int;
using ll = long long;
using lll = __int128;
using ld = long double;
// Pairs
using pii = pair<int, int>;
using psi = pair<si, si>;
using pll = pair<ll, ll>;
using plll = pair<lll, lll>;
using pld = pair<ld, ld>;
#define fi first
#define se second
// For
#define Frue(i, n, N) for (int i = (n); i <= (N); i++)
#define Fru(i, n, N) for (int i = (n); i < (N); i++)
#define Frde(i, n, N) for (int i = (n); i >= (N); i--)
#define Frd(i, n, N) for (int i = (n); i > (N); i--)
// PBDS
template<typename Z>
using ordered_set = tree<Z, null_type, less<Z>, rb_tree_tag, tree_order_statistics_node_update>;
// Various outputs
template<typename Y, typename Z> ostream& operator<<(ostream &os, const pair<Y, Z> &p) {
return os << '(' << p.fi << ',' << p.se << ')';
}
template<typename Z> ostream& operator<<(ostream &os, const vector<Z> &v) {
os << '{'; bool _first = 1;
for (auto &i : v) {if (!_first) os << ", "; os << i; _first = 0;}
return os << '}';
}
template<typename Z, unsigned long long sz> ostream& operator<<(ostream &os, const array<Z, sz> &arr) {
os << '{'; bool _first = 1;
for (auto &i : arr) {if (!_first) os << ", "; os << i; _first = 0;}
return os << '}';
}
// Quick macro functions
#define sqr(x) ((x)*(x))
#define debug(x) cout << #x << " = " << (x) << '\n'
#define debugV(v, x) cout << #v << "[" << (x) << "] = " << (v[x]) << '\n'
#define rrebug(x) cerr << #x << " = " << (x) << '\n'
#define rrebugV(v, x) cerr << #v << "[" << (x) << "] = " << (v[x]) << '\n'
#define All(x) x.begin(), x.end()
#define Sort(x) sort(All(x))
#define Reverse(x) reverse(All(x))
#define Uniqueify(x) Sort(x); x.erase(unique(All(x)), x.end())
#define RandomSeed chrono::steady_clock::now().time_since_epoch().count()
#define MultipleTestcases int _tc; cin >> _tc; for (int _cur_tc = 1; _cur_tc <= _tc; _cur_tc++)
// Check min and max
template<typename Z> void chmin(Z &a, Z b) {a = min(a, b);}
template<typename Z> void chmax(Z &a, Z b) {a = max(a, b);}
// Modular arithmetic
template<int MOD>
class ModInt {
public:
int v;
ModInt() : v(0) {}
ModInt(long long _v) {
v = int((-MOD < _v && _v < MOD) ? (_v) : (_v % MOD));
if (v < 0) v += MOD;
}
friend bool operator==(const ModInt &a, const ModInt &b) {return a.v == b.v;}
friend bool operator!=(const ModInt &a, const ModInt &b) {return a.v != b.v;}
friend bool operator< (const ModInt &a, const ModInt &b) {return a.v < b.v;}
friend bool operator<=(const ModInt &a, const ModInt &b) {return a.v <= b.v;}
friend bool operator> (const ModInt &a, const ModInt &b) {return a.v > b.v;}
friend bool operator>=(const ModInt &a, const ModInt &b) {return a.v >= b.v;}
ModInt &operator+=(const ModInt &a) {if ((v += a.v) >= MOD) v -= MOD; return *this;}
ModInt &operator-=(const ModInt &a) {if ((v -= a.v) < 0) v += MOD; return *this;}
ModInt &operator*=(const ModInt &a) {v = 1ll * v * a.v % MOD; return *this;}
ModInt &operator/=(const ModInt &a) {return (*this) *= inverse(a);}
friend ModInt pow(ModInt a, long long x) {
ModInt res = 1;
for (; x; x /= 2, a *= a) if (x & 1) res *= a;
return res;
}
friend ModInt inverse(ModInt a) {return pow(a, MOD - 2);}
ModInt operator+ () const {return ModInt( v);}
ModInt operator- () const {return ModInt(-v);}
ModInt operator++() const {return *this += 1;}
ModInt operator--() const {return *this -= 1;}
friend ModInt operator+(ModInt a, const ModInt &b) {return a += b;}
friend ModInt operator-(ModInt a, const ModInt &b) {return a -= b;}
friend ModInt operator*(ModInt a, const ModInt &b) {return a *= b;}
friend ModInt operator/(ModInt a, const ModInt &b) {return a /= b;}
friend istream &operator>>(istream &is, ModInt &v) {return is >> v.v;}
friend ostream &operator<<(ostream &os, const ModInt &v) {return os << v.v;}
};
const int ModA = 998244353;
const int ModC = 1e9 + 7;
using MintA = ModInt<ModA>;
using MintC = ModInt<ModC>;
// Other constants
const ll INF = 1e18;
const ll iINF = 1e9;
const ld EPS = 1e-9;
const ld iEPS = 1e-6;
const int maxN = 3e5 + 5;
const ll maxA = 1e9;
ll N, K, A[maxN], pf[maxN];
pll dp[maxN];
pll sub(pll x, pll y) {return {x.fi - y.fi, x.se - y.se};}
pll calc(ll C) {
// debug(C);
dp[0] = {0, 0};
pll mx = {pf[N], 0};
for (int i = 1; i <= N; i++) {
dp[i] = max(
dp[i-1],
sub(mx, {pf[N] - pf[i] + C, -1})
);
chmax(mx, {dp[i].fi + pf[N] - pf[i], dp[i].se});
// debugV(dp, i);
}
// debug(dp[N]);
return dp[N];
}
int main() {
ios_base::sync_with_stdio(false); cin.tie(NULL);
cin >> N >> K;
Frue(i, 1, N) {
cin >> A[i];
pf[i] = pf[i-1] + A[i];
}
// Find max(F) -> because F is convex, max(F) is G_0
pll hmx = calc(0);
// debug(hmx);
if (hmx.se <= K) {
cout << hmx.fi << '\n';
return 0;
}
// Find max X s.t. dF(K) <= X
// Binser on X
ll l = -maxA, r = maxA, ans, bt;
while (l <= r) {
ll m = (l + r) / 2;
// Find max Y s.t. dF(Y) >= m
pll Y = calc(m);
if (Y.se < K) {
r = m-1;
} else {
ans = m;
bt = Y.fi + K * ans;
l = m+1;
}
}
cout << bt << '\n';
}
