#include <fstream>
#include <queue>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
deque<pair<int, int> > q;
int main()
{
    int n, k;
    long long ans = 0;
    cin >> n >> k;
    for(int i = 1; i <= n; ++i) {
        int x;
        cin >> x;
        while(!q.empty() && q.back().second >= x) {
            q.pop_back();
        }
        q.push_back({i, x});
        if(q.front().first <= i - k) {
            q.pop_front();
        }
        if(i >= k) {
            ans = ans + q.front().second;
        }
    }
    cout << ans;
    return 0;
}