#include <bits/stdc++.h>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

long long n,k,minim = INT_MAX,s;

int V[5000010];

deque < pair <int,int> > q;

int main()
{
    fin>>n>>k;
    for(int i = 1;i<=n;i++)
        fin>>V[i];
    for(int i = 1;i<=n;i++)
    {
        if(!q.empty() && (i - q.front().second) >=k)
            q.pop_front();
        if(!q.empty())
        {
            if(V[i]<=q.back().first)
            {
                while(V[i]<q.back().first && !q.empty())
                    q.pop_back();
            }
            q.push_back(make_pair(V[i],i));
        }
        else
            q.push_back(make_pair(V[i],i));
        if(i>=k && !q.empty())
            s+=q.front().first;
    }
    fout<<s;
}