#include<fstream>
#define dim 5000007
using namespace std;


ifstream f("deque.in");
ofstream g("deque.out");

long long s;
int n,k,front,back,i;
int v[dim],dq[dim];

int main () {
	
	f>>n>>k;
	
	
	for(i=1;i<=n;i++)
		f>>v[i];
	
	front=1;
	back=0;
	for(i=1;i<=n;i++){
		
		
		while(front<=back && v[i]<=v[dq[back]])
			--back;
		
		dq[++back]=i;
		
		if(dq[front]==i-k)
			front++;
		
		if(i>=k)
			s+=v[dq[front]];
	}
	
	g<<s<<"\n";
	
	
	return 0;
}