#include <cstdio>
#include <deque>
using namespace std;

deque <long> deq;

long N, K, i, A[5000001];
long long s;
int main() {
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	
		scanf("%ld %ld", &N, &K);
		
		for (i = 1; i <= N; ++i) {
			scanf("%ld", &A[i]);
		}
		
		for (i = 1; i <= N; ++i) {
			while (!deq.empty() && A[i] <= A[deq.back()]) 
				deq.pop_back();
			
			deq.push_back(i);
			
			if (deq.front() == i-K) 
				deq.pop_front();
			
			if (i >= K)
				s += A[deq.front()];
		}
		
		printf("%lld\n", s);
	
	return 0;
}