#include <stdio.h>
#include <stdlib.h>

#define MAXN 5000000

int v[MAXN + 1];
int deq[MAXN + 1];

int main()
{
    FILE *fin, *fout;
    fin = fopen("deque.in", "r");
    fout = fopen("deque.out", "w");
    int N, K, i, st = 1, poz = 0, nr;
    long long sum = 0;
    fscanf(fin, "%d%d", &N, &K);
    for (i = 1; i < K; i++)
    {
				fscanf(fin, "%d", &v[i]);
				while (st <= poz && v[deq[poz]] > v[i])
				{
						poz--;
				}
				deq[++poz] = i;
		}
		for (i = K; i <= N; i++)
		{
				fscanf(fin, "%d", &v[i]);
				while (st <= poz && v[deq[poz]] > v[i])
				{
						poz--;
				}
				deq[++poz] = i;
				while (deq[st] < i - K + 1)
				{
						st++;
				}
				sum += v[deq[st]];
		}
		fprintf(fout, "%lld", sum);
    fclose(fin);
    fclose(fout);
    return 0;
}