#include <fstream>

using namespace std;

ifstream cin ("deque.in");
ofstream cout ("deque.out");

int main()
{
    int n, k;
    cin >> n >> k;

    int v[n + 1];
    for (int i = 1; i <= n; ++i){
        cin >> v[i];
    }

    long long s = 0;
    int coada[k + 1];
    int sf = 0, inc = 1;

    for (int i = 1; i <= n; ++i){

        while (sf >= inc and v[i] <= v[coada[sf]])
            --sf;
        coada[++sf] = i;
        if(i>=k)
        {
            if(i-coada[inc]+1>k)
                inc++;
            s += v[coada[inc]];
        }



        }


    cout << s;

    return 0;
}