#include <iostream>
#include <deque>
#include <fstream>

using namespace std;

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

const int maxN = 5e6 + 5;

deque <int> d;
int v[maxN];

signed main()
{
    int n, k;
    fin >> n >> k;

    long long ans = 0;
    for(int i = 1; i <= n; ++i) {

        fin >> v[i];

        if(i > k) {
            if(v[i-k] == d.back())
                d.pop_back();
        }

        while(v[i] < d.front() && !d.empty())
            d.pop_front();
        d.push_front(v[i]);

        if(i >= k)
            ans = ans + 1ll * d.back();
    }

    fout << ans;

    return 0;
}