#include <stdio.h>
#include <deque>

using namespace std;

#define DIM 5000010

int V[DIM];
long long S;
deque<int> D;
int N, K, i;

int main() {
	FILE *f = fopen("deque.in","r");
	fscanf(f,"%d %d",&N, &K);
	for (i=1;i<=N;i++) {
		fscanf(f,"%d",&V[i]);
		while (!D.empty() && V[i]<=V[D.back()] )
			D.pop_back();
		D.push_back(i);
		if (i>K && i-D.front() == K)
			D.pop_front();
		if (i>=K)
			S+=V[D.front()];
	}
	fclose(f);
	FILE *g = fopen("deque.out","w");
	fprintf(g,"%lld",S);
	fclose(g);
	
	return 0;
}