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

ifstream fin ("deque.in");
ofstream fout ("deque.out");
int n, k, v[5000001];
long long s;

deque <int> dq; //aici punem doar pozitiile din vector

int main(){
    int i, minim;
    fin >> n >> k;
    for (i = 1; i<= n; i++)
        fin >> v[i];
    for(i = 1; i<= n; i++)
    //adaugam nou element
    {
        while(dq.empty()==0 && v[dq.back()] >= v[i])
            dq.pop_back();
        dq.push_back(i);

        if(i >= k)
        {
            if (dq.front() < i-k+1) //nu este in ultimele k elemente
                dq.pop_front();
            minim = v[dq.front()];
            s += minim;
        }
    }

    fout<<s;
    return 0;   
}