#include <cstdio>
#define Nmax 5000010
using namespace std;

FILE *fi = fopen("deque.in", "r");
FILE *fo = fopen("deque.out", "w");
int n;
int k;
int v[Nmax];
int q[Nmax];
int in;
int sf;
long long s = 0;

int main()
{
	fscanf(fi, "%d%d", &n, &k);
	for (int i = 1; i<=n; i++)
		fscanf(fi, "%d", &v[i]);
	in = 1;
	sf = 0;
	
	for (int i = 1; i<=n; i++)
	{
		while (in <= sf && v[i] <= v[q[sf]]) sf--;
		q[++sf] = i;
		if (q[in] == i-k) in++;
		if (i >= k) s += v[q[in]];
	}
	
	fprintf(fo, "%lld", s);
	
	return 0;
}