#include <fstream>
using namespace std;

int dq[5000010],v[5000010];


ifstream cin("deque.in");
ofstream cout("deque.out");
int main()
{
    long long s=0;
    int n,k,i,p=0,poz=1;
    cin>>n>>k;
    for(i=1;i<=n;i++)
    {
        cin>>v[i];
        while(v[dq[p]]>=v[i]&&p>=poz)
            p--;
        dq[++p]=i;
        if(i>=k)
        {
            if(i-dq[poz]>=k)
                poz++;
            s=s+v[dq[poz]];
        }
    }
    cout<<s;
    return 0;
}