#include <iostream>
#include <fstream>
using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

int v[5000001], coada[5000001];
int main()
{
    int n, i, st = 0, dr = 0, k;
    long long s = 0;
    in >> n >> k;
    for(i = 1; i <= n; i++){
        in >> v[i];
        if(i < k){
            while(v[i] < v[coada[dr]] && st <= dr){
                dr--;
            }
            dr++;
            coada[dr] = i;
        }
        else{
            if(i - k >= coada[st]){
                st++;
            }
            while(v[i] < v[coada[dr]] && st <= dr){
                dr--;
            }
            dr++;
            coada[dr] = i;
            s += v[coada[st]];
        }
    }
    out << s;
    return 0;
}