#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
const int N=5000000;
int v[N],dq[N];
int main()
{
    int n,k,st=0,dr=-1;
    long long suma=0;
    in>>n>>k;
    for(int i=0; i<n; i++)
    {
        in>>v[i];
        if(st<=dr && dq[st]==i-k)
        {
            st++;
        }
        while(st<=dr && v[i]<=v[dq[dr]])
        {
            dr--;
        }
        dq[++dr]=i;
        if(i>=k-1)
        {
            suma+=v[dq[st]];
        }
    }
    out<<suma;

    return 0;
}