#include <stdio.h>
#include <deque>
using namespace std;
FILE *f=fopen ("deque.in", "r");
FILE *g=fopen ("deque.out", "w");
int v[5000001],i,n,k;
long long S;
deque <int> dq;

void adaugare(int x) {

while (!dq.empty() && x<=v[dq.back()] )
	dq.pop_back();

dq.push_back(i);
}

int main() {
fscanf (f, "%d%d", &n,&k);

for (i=1;i<=n;++i)
{
	fscanf (f, "%d", &v[i]);
	adaugare(v[i]);
	
	if (i>=k)
		S+=v[dq.front()];
	
	if (dq.front()==i-k)
		dq.pop_front();
}

fprintf (g, "%lld", S);
return 0;
}