#include<bits/stdc++.h>
using namespace std;
#define mod 1000000007
#define pb push_back
#define mp make_pair
#define Int long long
#define fs first
#define sc second
#define gcd __gcd
#define inf 1e15
Int dp[10004],c[10004],Hash[10004];
int main(){
	
	/*string s;
	cin>>s;
	int n = s.size();
	if(s[n-1]=='E'){
		cout<<n-1<<endl;
		return 0;
	}
	if(s[0] == 'E'){
		cout<<0<<endl;
		return 0;
	}
	int i,a=-1,b=-1,c=-1;
	for(i=2;i<n-1;i++){
		if(s[i]=='E' && s[i-1]=='E' && s[i-2]=='O'){
			a = i;
			break;
		}
	}
	for(i=1;i<n-2;i++){
		if(s[i]=='E' && s[i+1]=='E' && s[i+2]=='O'){
			b = i;
			break;
		}
	}
	if(a==-1 && b==-1){
		for(i=1;i<n-1;i++){
			if(s[i]=='E' && s[i+1]=='E'){
				a = i;
				break;
			}
		}
		if(a==-1){
			for(i=n-2;i>=1;i--){
				if(s[i]=='E'){
					a = i;
					break;
				}
			}
			cout<<a<<endl;
		}else{
			cout<<a<<endl;
		}
	}else{
		for(i=1;i<n-1;i++){
			if(s[i]=='E' && s[i+1]=='E'){
				c = i;
				break;
			}
		}
		cout<<min(a,min(b,c))<<endl;
	}*/
	Int n,k,i,j,l,r,ans=0;
	scanf("%lld %lld",&n,&k);
	c[0]=inf;
	for(i=1;i<=n;i++){
		scanf("%lld",&c[i]);
		dp[i] = 0;
	}
	for(i=1;i<=n;i++){
		l = max(i-k,1LL);
		r = min(i+k,n);
		for(j=l;j<=r;j++){
			if(c[dp[j]]>=c[i]){
				dp[j] = i;
			}
		}
	}
	for(i=1;i<=n;i++){
		if(!Hash[dp[i]]){
			Hash[dp[i]] = 1;
			ans+= c[dp[i]];
		}
	}
	printf("%lld\n",ans);
	return 0;
}