#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#pragma GCC optimize ("O1")
#pragma GCC optimize ("O2")
#pragma GCC optimize ("O3")
#pragma GCC optimize ("Ofast")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target ("avx2")

using namespace std;
using namespace __gnu_pbds;

#define ordered_set tree <long long, null_type, less<long long>, rb_tree_tag, tree_order_statistics_node_update>
#define lsb(x)(x & (-x))

deque <pair <long long, long long>> dq;

void solve ()
{
    long long n, k, sum = 0;
    cin >> n >> k;
    for (long long i = 1; i < k; i++)
    {
        long long x;
        cin >> x;
        while (!dq.empty() && dq.back().first > x)
        {
            dq.pop_back();
        }
        dq.push_back({x, i});
    }
    for (long long i = k; i <= n; i++)
    {
        long long x;
        cin >> x;
        if (dq.front().second == i - k)
        {
            dq.pop_front();
        }
        while (!dq.empty() && dq.back().first > x)
        {
            dq.pop_back();
        }
        dq.push_back({x, i});
        sum += dq.front().first;
    }
    cout << sum;
    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;
}