#include <iostream>
#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
const int N=5000005;
int v[N],deque[N];
long s;
int st=1,dr,k,n;
void stanga(int i)
{
    if(i-deque[st] == k)
        st++;
}
void dreapta(int i)
{
    while(st<=dr && v[i]<=v[deque[dr]])
        dr--;
}
int main()
{
    in>>n>>k;
    for(int i=1;i<=n;i++)
        in>>v[i];
    for(int i=1;i<=n;i++)
    {
        if(i>k)
            stanga(i);
        dreapta(i);
        deque[++dr]=i;
        if(i>=k)
            s+=v[deque[st]];
    }
    out<<s;
    return 0;
}