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