#include <fstream>
#include <deque>
#include <cstdio>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
deque<int> dq;
int n,k,i,v[5000001];
long long sum;
int main()
{
    freopen("deque.in","r",stdin);
    scanf("%d%d",&n,&k);
    for(i=1; i<=n; i++)
    {
       scanf("%d",&v[i]);
        while(!dq.empty() && v[i]<v[dq.back()])
            dq.pop_back();
        if(dq.front()+k==i)
            dq.pop_front();
        dq.push_back(i);
        if(i>=k && !dq.empty())
            sum+=v[dq.front()];
    }
    freopen("deque.out","w",stdout);
    printf("%lld\n",sum);
}