#include <bits/stdc++.h>
#define int long long
using namespace std;
signed main()
{
    ifstream cin("deque.in");
    ofstream cout("deque.out");
    int n, k, s = 0;
    deque<pair<int, int>> dq;
    cin >> n >> k;
    for(int i = 1; i < k; i++){
        int a;
        cin >> a;
        while(dq.empty() == false && dq.back().first > a)
            dq.pop_back();
        dq.push_back({a, i});
    }
    for(int i = k; i <= n; i++){
        int a;
        cin >> a;
        while(dq.empty() == false && dq.back().first > a)
            dq.pop_back();
        if(dq.empty() == false && dq.front().second <= i - k)
            dq.pop_front();
        dq.push_back({a, i});
        s += dq.front().first;
    }
    cout << s;
    return 0;
}