#include<cstdio>
const int maxn=100000001;
long long s;
int a[maxn], deque[maxn], i, k, n, first, last;

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]);
	
	first=1, last=0;
	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]];
	                    }
	
	printf("%lld\n", s);
	
	fclose(stdin);
	fclose(stdout);
	return 0;
}