#include <fstream>
using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");
int n,k,i,A[5000010],D[5000010],st,dr,j;
long long s;

int main(){
	fin>>n>>k;
	for (i=1;i<=n;i++)
		fin>>A[i];

	st=1;
	dr=0;
	for (i=1;i<=n;i++){
		while (st<=dr && A[i]<=A[D[dr]])
                dr--;
		D[++dr]=i;

		if(D[st]==i-k)
            st++;
	/*	for(j=st;j<=dr;j++)
		fout<<A[D[j]]<<" ";
		fout<<"\n"; */
		if (i>=k)
            s+=A[D[st]];
	}

	fout<<s;

	return 0;
}