洛谷P1792

#include <bits/stdc++.h>
/*
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/hash_policy.hpp>
*/
using namespace std;

const double eps = 1e-10;
const double pi = 3.1415926535897932384626433832795;
const double eln = 2.718281828459045235360287471352;

#define f(i, a, b) for (int i = a; i <= b; i++)
#define scan(x) scanf("%d", &x)
#define mp make_pair
#define pb push_back
#define lowbit(x) (x&(-x))

#define fi first
#define se second
#define SZ(x) int((x).size())
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define summ(a) (accumulate(all(a), 0ll))

typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef vector<int> vi;

using ll=long long;

ll n,m,a[(int)4e5+9],l[(int)4e5+9],r[(int)4e5+9],ans;
bitset<(int)5e5+9> vis;
priority_queue<pair<ll,ll>>q;
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin>>n>>m;
    f(i,1,n)cin>>a[i];
    if(2*m>n){
        cout<<"Error!\n";
        return 0;
    }
    for(int i=1;i<=n;++i)l[i]=(n+i-2)%n+1,r[i]=(n+i)%n+1;
    for(int i=1;i<=n;++i)q.push({a[i],i});
    while(!q.empty()&&m){
        auto [aa,bb]=q.top();
        q.pop();
        if(vis[bb])continue;
        vis[bb]=vis[l[bb]]=vis[r[bb]]=1,ans+=aa,n+=1,m-=1,a[n]=a[l[bb]]+a[r[bb]]-a[bb];
        l[n]=l[l[bb]],r[n]=r[r[bb]],r[l[n]]=n,l[r[n]]=n;
        q.push({a[n],n});
    }
    cout<<ans;
    return 0;
}