#include <fstream>

using namespace std;

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

int main()
{
    long long n, k;
    in >> n >> k;
    long long v[n], d[n], st = 0, dr = -1, sum = 0;
    for(int i = 0; i < n; i++)
    {
        in >> v[i];
        if(st <= dr && d[st] == i - k)
        {
            st++;
        }
        while(st <= dr && v[i] <= v[d[dr]])
        {
            dr--;
        }
        d[++dr] = i;
        if(i >= k - 1)
        {
            sum += v[d[st]];
        }
    }
    out << sum << '\n';
    return 0;
}