#include <bits/stdc++.h>

using namespace std;

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

struct per{
    int val;
    int ind;
};

int main()
{
    int n, k, i, nr;
    long long suma;
    deque <per> dq;

    fin >> n >> k;

    suma = 0;
    for(i = 1; i <= n; i++){
        fin >> nr;

        while(!dq.empty() && dq.front().ind < i - k + 1){
            dq.pop_front();
        }
        while(!dq.empty() && dq.back().val >= nr){
            dq.pop_back();
        }

        per nou = {nr, i};
        dq.push_back(nou);
        if(i >= k){
            suma += dq.front().val;
        }
    }
    fout << suma << "\n";
    return 0;
}