#include <bits/stdc++.h>

using namespace std;

const int max_size = 5e6 + 20, rmax = 20;

deque <int> dq;
int v[max_size];

void solve ()
{
    int n, k;
    cin >> n >> k;
    long long ans = 0;
    for (int i = 1; i < k; i++)
    {
        cin >> v[i];
        while (!dq.empty() && v[dq.back()] >= v[i])
        {
            dq.pop_back();
        }
        dq.push_back(i);
    }
    for (int i = k; i <= n; i++)
    {
        cin >> v[i];
        if (dq.front() == i - k)
        {
            dq.pop_front();
        }
        while (!dq.empty() && v[dq.back()] >= v[i])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        ans += 1LL * v[dq.front()];
    }
    cout << ans;
    cout << '\n';
}

signed main ()
{
#ifdef LOCAL
    freopen("test.in", "r", stdin);
    freopen("test.out", "w", stdout);
#else
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
#endif // LOCAL
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    long long tt;
    //cin >> tt;
    tt = 1;
    while (tt--)
    {
        solve();
    }
    return 0;
}