#include <bits/stdc++.h>

using namespace std;
int w[5000010];
int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int n, k, i, val;
    long long sol = 0;
    ///val, poz
    deque <int> minim;



    fin >> n >> k;

    for(i = 1; i <= n; ++i){

        while(!minim.empty() && minim.front() < i - k + 1)
            minim.pop_front();

        fin >> w[i];

        while(!minim.empty() && w[minim.back()] >= w[i]){
            minim.pop_back();
        }
        minim.push_back(i);

        if(i >= k)
        sol += w[minim.front()];
    }

    fout << sol;

    return 0;
}