#include <fstream>
using namespace std;
const int N=5000000;

ifstream in("deque.in");
ofstream out ("deque.out");
int v[N], d[N];
int main()
{   int n ,k ,st, dr;
    long long s=0;
    in>>n>>k;
    st=0;
    dr=-1;
    for(int i=0;i<n;i++)
    {
        in>>v[i];

        if(st<=dr&&v[d[st]]==i-k;)
        {
            st++;
        }
        while (st<=dr && v[d[dr]]>=v[i])
        {
            dr--;
        }
        d[++dr]=i;
        if(i>=k-1)
        {
            s+=v[d[st]];
        }

    }
    in.close();
    out<<s;
    out.close()
    return 0;
}