#include <iostream>
#include <deque>
#include <fstream>

using namespace std;

deque <pair<int, int> > Q;

ifstream f("deque.in");
ofstream g("deque.out");

int main()
{
    int N, K, S = 0;
    pair<int, int> x;
    f >> N >> K;
    for(int i = 1; i <= K; i++)
    {
        f >> x.first;
        x.second = i;
        while(!Q.empty() && Q.back().first >= x.first)
            Q.pop_back();
        Q.push_back(x);
    }
    S += Q.front().first;
    Q.pop_front();

    for(int i = K + 1; i <= N; i++)
    {
        f >> x.first;
        x.second = i;
        while(!Q.empty() && Q.front().second <= i - K)Q.pop_front();
        while(!Q.empty() && Q.back().first >= x.first)
            Q.pop_back();
        Q.push_back(x);
        S += Q.front().first;
    }
    g << S;
    return 0;
}