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