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

ifstream cin("deque.in");
ofstream cout("deque.out");
const int dim= 5e6+ 5;
int v[dim];
deque <int> d;

int main()
{
    int n, k, i, j;
    cin >> n>> k;

    for(i= 1;i <= n;i++)
        cin >> v[i];

    long long rez= 0, mini= -1e9;
    for(i= 1;i <= k;i++){
        while(!d.empty() and v[d.back()] > v[i])
            d.pop_back();
        d.push_back(i);
    }
    rez+= v[d.front()];
    //cout << v[d.front()]<<" ";

    for(i= k+ 1;i <= n;i++){
        while(!d.empty() and d.front() < i- k+ 1)
            d.pop_front();
        while(!d.empty() and v[d.back()] > v[i])
            d.pop_back();
        d.push_back(i);
        rez+= v[d.front()];
        //cout << v[d.front()]<<" ";
    }
    //cout << endl;
    cout << rez;


    return 0;
}