#include <bits/stdc++.h>

using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");
#define cin fin
#define cout fout

#define N 100005
deque < pair < int , int > > v;
int n, k, s, nr;

int main()
{
    cin >> n >> k;
    for(int i = 1 ; i <= n ; i++)
    {
        cin >> nr;
        while(!v.empty() &&  v.front().second < i-k+1)
        {
            v.pop_front();
        }
        while(!v.empty()  &&  v.back().first > nr)
        {
            v.pop_back();
        }
        v.push_back({nr,i});
        if(i >= k)s += v.front().first;
    }
    cout << s;
    return 0;
}