#include <cstdio>
#include <iostream>

using namespace std;

const int N=5000000+7;
int n,k,a[N];

signed main() {
        freopen ("deque.in","r",stdin);
        freopen ("deque.out","w",stdout);


        scanf("%d%d",&n,&k);


        for (int i=1;i<=n;i++){
                scanf("%d",&a[i]);
        }

        long long sum=0;
        for (int i=k;i<=n;i++){
                int mn=a[i];
                for (int j=i-k+1;j<=i;j++){
                        mn=min(mn,a[j]);
                }
                sum+=mn;
        }


        printf("%lld\n",sum);

        return 0;
}

/**

**/