#include <bits/stdc++.h>
using namespace std;

#define int long long

signed main(){
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int N,K;
	cin>>N>>K;
	vector<int>v(N+1),pf(N+1);
	for(int i=0;i<N;i++){
		cin>>v[i];
		pf[i+1]=pf[i]+v[i];
	}
	auto cost=[&](int s,int e)->int{
		return (pf[e]-pf[s])*(e-s);
	};
	auto solve=[&](int y)->pair<int,int>{
		vector<int>dp(N+1,1e18),cnt(N+1);
		deque<int>q;
		int o=0;
		auto bs=[&](int l,int i)->int{
			int h=N;
			int ll=l;
			while(l<h){
				int m=(l+h)/2;
				if(dp[i]+cost(i,m)<=dp[o]+cost(o,m)){
					h=m;
				}
				else{
					l=m+1;
				}
			}
			return h;
		};
		dp[0]=-y;
		cnt[0]=-1;
		for(int i=1;i<=N;i++){
			while(!q.empty()){
				int j=q.front();
				if(dp[j]+cost(j,i)<dp[o]+cost(o,i)){
					o=j;
					q.pop_front();
				}
				else if(j<o){
					q.pop_front();
				}
				else{
					break;
				}
			}
			dp[i]=dp[o]+cost(o,i)+y;
			cnt[i]=cnt[o]+1;
			while(!q.empty()&&bs(i,i)<=bs(i,q.back())){
				q.pop_back();
			}
			q.push_back(i);
		}
		return{dp[N],cnt[N]};
	};
	int l=0,h=1e12;
	while(l<h){
		int m=(l+h)/2;
		auto [x,c]=solve(m);
		if(c<=K){
			h=m;
		}
		else{
			l=m+1;
		}
	}
	auto [x,c]=solve(h);
	cout<<x-c*h<<'\n';
	return 0;
}