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