#include<fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n, k, i, first = 1, last, a[5000001], deque[5000001];
long long s;
int main (){ 
	f>>n>>k;
	for (i = 1; i <= n; ++i) f>>a[i];
	for (i = 1; i <= n; ++i){
		while (first <= last && a[i] <= a [deque [last]]) --last;
		deque [++last] = i;
		if (deque [first] == i - k) ++first;
			if (i >= k) s += a [deque [first]];
	}
	g<<s<<'\n'; 
	g.close(); return 0;
}