#include <cstdio>
#include <cstdlib>
#include <deque>
#include <algorithm>
#include <iostream>
using namespace std;
int N,K,*a,sum;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d %d",&N,&K);
    a=(int*)malloc(N*sizeof(int));
    for(int i=0;i<N;i++)
        scanf("%d",a+i);
    deque<int>d;
    for(int i=0;i<K;i++)
        d.push_front(a[i]);
    sum+=*(min_element(d.begin(),d.end()));
    for(int j=K;j<N;j++)
    {
        d.pop_back();
        d.push_front(a[j]);
        sum+=*(min_element(d.begin(),d.end()));
    }
    printf("%d",sum);
    return 0;
}