#include <fstream>
using namespace std;
ifstream in ("deque.in");
ofstream out ("deque.out");
int const N=5000001;
int d[N],v[N],st=1,dr,n,k;
long long sum;

void stanga(int i)
{
    if(i-d[st]==k)
        st++;
}

void dreapta(int i)
{
    while(st<=dr && v[i]<=v[d[dr]])
        dr--;
    d[++dr]=i;
}

int main()
{
    int i;
    in>>n>>k;
    for(i=1;i<=n;i++)
        in>>v[i];
    for(i=1;i<=n;i++)
    {
        stanga(i);
        dreapta(i);
        if(i>=k) sum+=v[d[st]];
    }
    out<<sum;
    return 0;
}