#include <fstream>
using namespace std;
ifstream fin ("deque.in");
ofstream fout ("deque.out");
int n, k, i, f, b;
int v[100001], q[100001];
long long s;
int main(){
	fin>>n>>k;
	for(i=1;i<=n;i++)
		fin>>v[i];
        f=1;
        b=0;
	for(i=1;i<=n;i++){
		while(f<=b && v[i]<=v[q[b]])
            b--;
		q[++b]=i;
		if(q[f] == i-k)
            f++;
		if(i>= k)
		s+=v[q[f]];
	}
	fout<<s;
}