#include <bits/stdc++.h>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n, k;
int a[5000005];
deque<int>dq;
long long sol;


int main()
{
    int i;
    fin >> n >> k;
    for(i = 1;i <= n;i++)
        fin >> a[i];
    for(i = 1;i <= k;i++)
    {
        if(!dq.empty())
        {
            while(a[dq.back()] > a[i])
                dq.pop_back();
            dq.push_back(i);
        }
        else
            dq.push_back(i);
    }
    sol += a[dq.front()];
    for(i = k + 1;i <= n;i++)
    {
        if(!dq.empty() && (dq.front() < i - k + 1))
            dq.pop_front();
        if(!dq.empty())
            while(!dq.empty() && a[dq.back()] > a[i])
                dq.pop_back();
        dq.push_back(i);
        sol += a[dq.front()];
    }
    fout << sol << "\n";
    return 0;
}