#include <fstream>

using namespace std;
int main()
{
    ifstream in("deque.in");
    ofstream out("deque.out");
    int n,k,rez=0,d[5000001],f=1,b=0;
    int v[5000001];
    in >> n;
    in >> k;
    for(int i=1;i<=n;i++){
        in >> v[i];
    }
     for(int i=1;i<=n;i++){
            while(f<=b && v[i]<=v[d[b]])
                b--;
            d[++b]=i;
            if(d[f]==i-k)f++;
            if(i>=k)rez+=v[d[f]];

    }

    out << rez;
    return 0; ////    1 3
}