#include<fstream>
#define maxn 5000010
using namespace std;

int n, k, st, dr;
int a[maxn], deq[maxn];
long long s=0;

int main()
{
    int i;
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>a[i];
    st=1, dr=0;
    for(i=1;i<=n;i++)
    {
        while(st<=dr && a[i] <= a[deq[dr]])
            dr--;
        deq[++dr]=i;
        if(deq[st]==i-k)
            st++;
        if(i>=k)
            s+=a[deq[st]];
    }
    fout<<s;
    return 0;
}