#include <fstream>
#include <deque>
#define ind first
#define val second

using namespace std;
typedef long long ll;

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

const int NMAX = 5000005;
int v[NMAX];

ll n, k;
deque < pair <int, int> > deck;
ll ans;

int main()
{
    fin >> n >> k;
    for(int i = 1; i <= n; i++)
        fin >> v[i];

    int i;
    for(i = 1; i < k; i++) {
        while(!deck.empty() && deck.back().val > v[i])
            deck.pop_back();

        deck.push_back({i, v[i]});
    }

    for(i = k; i <= n; i++) {
        while(!deck.empty() && deck.back().val > v[i])
            deck.pop_back();

        deck.push_back({i, v[i]});
        while(!deck.empty() && deck.front().ind < i - k + 1)
            deck.pop_front();

        ans += deck.front().val;
    }
    fout << ans;
    return 0;
}