#include<stdio.h>
#define maxn 5000001
using namespace std;
int dq[maxn],poz[maxn];
int n,k;
long long s=0;
void deque_solve(){
	int f=1,b=0;
	for(int i=1;i<=n;i++){
		scanf("%d",&poz[i]);
		while(f<=b && poz[dq[b]]>=poz[i])
			b--;
		dq[++b]=i;
		if(i>=k){
			if((i-dq[f])==k)
			++f;
			s+=poz[dq[f]];
		}
		
	}
}


int main(){
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%d%d",&n,&k);
	deque_solve();
	printf("%lld",s);
	return 0;
}