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| #include<bits/stdc++.h>
#define ll long long
#define int long long
#define ull unsigned long long
#define maxn 200005
#define put() putchar('\n')
#define Tp template<typename T>
#define Ts template<typename T,typename... Ar>
using namespace std;
Tp void read(T &x){
int f=1;x=0;char c=getchar();
while (c<'0'||c>'9') {if (c=='-') f=-1;c=getchar();}
while (c>='0'&&c<='9') {x=x*10+c-'0';c=getchar();}
x*=f;
}
namespace Debug{
Tp void _debug(char* f,T t){cerr<<f<<'='<<t<<endl;}
Ts void _debug(char* f,T x,Ar... y){while(*f!=',') cerr<<*f++;cerr<<'='<<x<<",";_debug(f+1,y...);}
#define gdb(...) _debug((char*)#__VA_ARGS__,__VA_ARGS__)
}using namespace Debug;
#define fi first
#define se second
#define mk make_pair
const int mod=1e9+7;
ll power(ll x,int y=mod-2,int p=mod) {
ll sum=1;x%=p;
while (y) {
if (y&1) sum=sum*x%p;
x=x*x%p;y>>=1;
}
return sum;
}
int n,m;
int ans,a[maxn];
int nex[maxn],pre[maxn],vis[maxn];
priority_queue<pair<int,pair<int,int> > >q;
void del(int x) {
pre[nex[x]]=pre[x];
nex[pre[x]]=nex[x];
vis[x]=1;
}
void add(int x) {
if (x&&x<n&&nex[x]&&nex[x]<n) {
q.push(mk(a[x]+a[nex[x]],mk(x,nex[x])));
}
}
signed main(void){
int i;
read(n);read(m);
m=min(m,n-m);
for (i=1;i<n;i++) read(a[i]);
if (2*m==n) {
for (i=1;i<n;i++) ans+=a[i];
printf("%lld\n",ans);
return 0;
}
for (i=1;i<n;i++) nex[i]=i+1,pre[i]=i-1;
for (i=1;i<n-1;i++) q.push(mk(a[i]+a[i+1],mk(i,i+1)));
while (!q.empty()) {
auto tmp=q.top();q.pop();
if (vis[tmp.se.fi]||vis[tmp.se.se]) continue;
ans+=tmp.fi;if (--m==0) break;
int x=tmp.se.fi,y=tmp.se.se;
del(x),del(y);
add(pre[x]),add(nex[y]);
}
printf("%lld\n",ans);
return 0;
}
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