#include <bits/stdc++.h>
using namespace std;
ifstream f ("deque.in");
ofstream g ("deque.out");
deque <long long> mini;
long long n, k, sum, v[5000005];
int main()
{

    f >> n >> k;
    for (int i = 1; i <= n; i++)
    {
        f >> v[i];
        while (!(mini.empty()) && v[i] < mini.back())
        {
            mini.pop_back();
        }
        mini.push_back(v[i]);

        if (i > k)

        {
            if (v[i-k] == mini.front())
                mini.pop_front();


        }
        if(i >= k)
            sum += mini.front();
    }
    g<<sum;

    return 0;
}