#include<bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
const int MAXN = 5000005;
int n, m;
deque<pair<int, int> > q;
int main()
{   long long sol = 0;
    fin >> n >> m;
    for (int i = 1; i <= n; ++i)
    {   int k;
        fin >> k;
        while (!q.empty() && k < q.back().first) q.pop_back();
        if (i >= m)
        {   while (!q.empty() && q.front().second <= i - m) q.pop_front(); }
        q.push_back({k, i});
        if (i >= m) sol += (long long)q.front().first;
    }
    fout << sol;
    fout.close(); return 0;
}