#include <iostream>
#include <fstream>
#include <deque>
const int MAX = 5000005;
using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");
int v[MAX];
deque <int> p;
int main()
{
    long long n,k,sum = 0;
    f >> n >> k;
    for(int i = 1; i <= n; i++)
        f >> v[i];
    for(int i = 1; i <= n; i++){
        while(!p.empty() && v[i] <= v[p.back()]){
            p.pop_back();
        }
        p.push_back(i);
        if(p.front() == i - k)
            p.pop_front();
        if(i >= k)
            sum = v[p.front()] + sum;
    }
    g << sum;
    return 0;
}