#include <stdio.h>
#define DIM 5000002

int a[DIM];
int n, k, i ,j, mink;
long long s;

int main(){
	
	freopen ("deque.in", "r", stdin);
	freopen ("deque.out", "w", stdout);
	
	scanf ("%d %d", &n, &k);
	for (i=1; i<=n; i++)
		scanf ("%d", &a[i]);

	mink = a[0] = 0;
	for (i=1; i<=n-k+1; i++){
		if (mink == a[i-1]){
			mink = a[i];
			for (j=1; j<k; j++)
				if (mink > a[i+j])
					mink = a[i+j];
		} else if (mink > a[i+k-1]) mink = a[i+k-1];
		s += (long long)mink;
	}
	
	printf ("%lld", s);
	
	return 0;
}