#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n,k,v[5000011],deq[5000011];

int main(void){
	register int i,j,p,u,aux;
	
	f>>n>>k;
	
	p=u=1,deq[1]=1;
	long long s=0;
	f>>v[1];
	for(i=2;i<=n;i++){
		f>>v[i];
		deq[++u]=i;
		while(v[deq[u]]>=v[i] && u>=p)
			u--;
		deq[++u]=i;
		if(deq[u]-deq[p]==k)
			p++;
		if(i>=k)
			s+=v[deq[p]];
		
	}
	
	g<<s;
	return 0;
}