#include <fstream>
#define MAX 6000005

using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");
int n, k, v[MAX], Deque[MAX];
long long s;

int main()
{
    int i;
    fin >> n >> k;
    for (i = 1; i <= n; i++)
        fin >> v[i];
    int Front = 1, Back = 0;
    for (i = 1; i <= n; i++) {
        while (Front <= Back && v[i] <= v[ Deque[Back] ])
            Back--;

        Deque[++Back] = i;

        if (Deque[Front] == i-k) Front++;

        if (i >= k) s += v[ Deque[Front] ];
    }
    fout << s;
    return 0;
}