#include<fstream>
#include<deque>
#include<iostream>
using namespace std;


typedef struct { int x,pos; } nr;



deque<nr> q;
void add_q(nr x){
    while(!q.empty() && q.back().x>=x.x)
    {
        //  cout<<q.back()<<' ';
          q.pop_back();

    }
    q.push_back(x);
}


int main(){
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int n,i,k;
    nr x;
    long long s=0;
    fin>>n>>k;
    for(i=1;i<=k;++i)
        {
            fin>>x.x;x.pos=i;
            add_q(x);
        }
    s+=q.front().x;
    for( i=k+1;i<=n;++i){
            fin>>x.x; x.pos=i;
            if(q.front().pos==i-k)
                q.pop_front();
            add_q(x);
            s+=q.front().x;
    }
    fout<<s;
    return 0;
}