#include <bits/stdc++.h>
using namespace std;

int v[5000005];
deque<int>dq;
int main()
{
    ifstream cin("deque.in");
    ofstream cout("deque.out");
    
    int n, k, s=0;
    cin>>n>>k;
    for(int i=1; i<=n; i++)
    {
        cin>>v[i];
        while(!dq.empty() && dq.front()==i-k)
        dq.pop_front();
        while(!dq.empty() && v[i]<=v[dq.back()])
        dq.pop_back();
        dq.push_back(i);
        if(i>=k)
        {
            //cout<<dq.front()<<'\n';
            s=s+v[dq.front()];
        }
    }
    cout<<s;

    return 0;
}