#include <fstream>

using namespace std;
ifstream in ("deque.in");
ofstream out ("deque.out");
const int N=5000003;
int v[N],d[N];
int main()
{
    int n,k,i,s=0,st=0,dr=-1;
    in>>n>>k;
    for (i=0;i<n;i++)
        in>>v[i];
    for (i=0;i<n;i++)
    {
        if (st<=dr && d[st]==i-k)
            st++;
        while (st<=dr && v[i]<=v[d[dr]])
            dr--;
        dr++;
        d[dr]=i;
        if (i>=k-1)
            s+=v[d[st]];
    }
    out<<s;
    return 0;
}