#include<iostream>
#include<fstream>
#include<vector>
#include<stack>
#include<deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,i,j,s,v[5000005],minn,x,minnou;
deque<int> q;
int main()
{
    fin>>n>>k;
    minn=10000000;
    for(i=1;i<=n;i++)
    {
        fin>>v[i];
    }
    for(i=1;i<=n;i++)
    {
        while(!q.empty() && v[i]<=v[q.back()])
        {
            q.pop_back();
        }
        q.push_back(i);
        if(q.front()==i-k)
            q.pop_front();
        if(i>=k)
        {
            s=s+v[q.front()];
        }
    }
    fout<<s;
    fin.close();
    fout.close();
    return 0;
}