#include <fstream>

using namespace std;


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

const int N = 5000000;

int v[N],fg[N];

int main()
{
    int st = 0,dr = -1,x,z;
    long long m = 0;
    in >> x >> z;
    for (int y=0; y < x; y++ )
    {
        in >> v[y];
        if(st <= dr && fg[st] == y - z)
            st ++;
        while (st <= dr && v[y] <= v[fg[dr]])
            dr --;
        fg[++dr] = y;
        if(y >= z - 1)
            m = m + v[fg[st]];

    }
    out << m;


    return 0;
}