#include<fstream>
#include<vector>
using namespace std;
int n,k,v[5000100],deque[5000100],l=1,r;
int main() {
	int i;
	long long s=0;
	ifstream in("deque.in");
	in>>n>>k;
	for(i=0;i<n;i++) {
		in>>v[i];
		while(l<=r&&v[i]<v[deque[r]])
			r--;
		deque[++r]=i;
		if(deque[l]==i-k)
			l++;
		if(i>k-2)
			s+=v[deque[l]];
		}
	ofstream out("deque.out");
	out<<s<<'\n';
	in.close();
	out.close();
	return 0;
}