#include <bits/stdc++.h>
using namespace std;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int n,k,nr,i;
    deque<int>d;
    deque<int>poz;
    long long sum=0;
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;i++)
    {
        scanf("%d",&nr);
        while(!d.empty()&&d.back()>=nr)
        {
            d.pop_back();
            poz.pop_back();
        }
        d.push_back(nr);
        poz.push_back(i);
        if(i>=k)sum+=d.front();
        if(i>=k)
            if(poz.front()==(i-k+1))poz.pop_front(),d.pop_front();
    }
    cout<<sum;
    return 0;
}