#ifdef NACHIA
#define _GLIBCXX_DEBUG
#else
#define NDEBUG
#endif
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <queue>
using i64 = long long;
using u64 = unsigned long long;
#define rep(i,n) for(i64 i=0; i<i64(n); i++)
const i64 INF = 1001001001001001001;
template<typename A> void chmin(A& l, const A& r){ if(r < l) l = r; }
template<typename A> void chmax(A& l, const A& r){ if(l < r) l = r; }
using namespace std;

void testcase(){
    i64 N, K; cin >> N >> K;
    vector<i64> A(N+1);
    rep(i,N) cin >> A[i];
    rep(i,N-1) A[i+1] += A[i];
    priority_queue<i64> que;
    i64 f = 0;
    i64 ans = -INF*4;
    rep(i,N){
        if(i64(que.size()) == K-1) chmax(ans, A[i]*K - f);
        que.push(A[i]); f += A[i];
        if(i64(que.size()) >= K){
            f -= que.top();
            que.pop();
        }
    }
    cout << ans << "\n";
}

int main(){
    ios::sync_with_stdio(false); cin.tie(nullptr);
    testcase();
    return 0;
}