# include <stdio.h>
int v[5000000], deque[5000000];
int n, k, i, st, dr;
long long s = 0;
int main (){
	freopen ("deque.in", "r", stdin);
	freopen ("deque.out", "w", stdout);
	scanf ("%d%d", &n, &k);
	for (i = 1, st = 1; i <= n; ++i){
		scanf ("%d", &v[i]);
	}
	for (i = 1, st = 1; i <= n; ++i){
	    for (; st <= dr && v[i] <= v[deque[dr]]; --dr);
		deque[++dr] = i;
		if (deque[st] == i - k) ++st;
		if (i >= k) s += v[deque[st]];
	}
	printf ("%lld\n", s);
	return 0;
}