#include <bits/stdc++.h>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
#define pb push_back
#define ll long long
#define pf push_front
const int Nmax = 5000000 + 5;
deque<ll> dq;
ll n, k, a[Nmax], s;

int main()
{
    fin >> n >> k;
    for(int i = 1; i <= n; ++i) fin >> a[i];

    for(int i = 1; i <= n; ++i)
    {
        while(!dq.empty() && a[i] < a[dq.back()])
            dq.pop_back();

        dq.push_back(i);

        if(dq.front() == i - k)dq.pop_front();

        if(i >= k)
        s += a[dq.front()];
    }

    fout << s;
    return 0;
}