#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
const int N=5000001;
int v[N],n,d[N],st=1,dr=0,k;
void stanga(int i)
{
    if(i-d[st]==k)
        st++;
}
void dreapta(int i)
{
    while(st<=dr&&v[i]<=v[d[dr]])
    dr--;
}
int main()
{
    int i;
    long long sum=0;
    f>>n>>k;
    for(i=1;i<=n;i++)
    f>>v[i];
    for(i=1;i<=n;i++)
    {
        dreapta(i);
        d[++dr]=i;
        stanga(i);
        if(i>=k) sum+=v[d[st]];

    }
    g<<sum;
}