#include <iostream>
#include <fstream>

using namespace std;
int v[5000001], Deque[5000001], st, dr, N, K;
ifstream f ("deque.in");
ofstream g ("deque.out");
long long S;
int main()
{

    int i;
    f>>N>>K;
    for(i=1; i<=N; i++)
        f>>v[i];
    st=1;
    dr=0;
    for(i=1; i<=N; i++)
    {
        while((st<=dr)&&(v[i]<=v[Deque[dr]]))
            dr--;
        Deque[++dr]=i;
        if(Deque[st]==i-K)
            st++;
        if(i>=K)
            S+=v[Deque[st]];
    }
    g<<S;
    return 0;
}