#include <iostream>
#include <fstream>
using namespace std;
ifstream in ("deque.in");
ofstream out("deque.out");
int const N=5000009;
int n,k,s,v[N];
int dr,st,d[N];
inline void stanga(int x)
{
    if(x-d[st]==k)  st++;
}
inline void dreapta(int x)
{
    while(st<=dr && v[x]<=v[d[dr]])
        dr--;
}
int main()
{
    in>>n>>k;
    st=1;
    dr=0;
    for(int i=1;i<=n;i++)
        in>>v[i];
    for(int i=1;i<=n;i++)
    {
        if(i>k) stanga(i);
        dreapta(i);
        d[++dr]=i;
        if(i>=k)
            s+=v[d[st]];
    }
    out<<s<<"\n";
    return 0;
}