#include <bits/stdc++.h>

using namespace std;

deque <int> q;
int a[5000005];
int n, k;
long long s;
int main()
{ int i, x;
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin >> n >> k;
    for(i = 1; i <= n; i++)
            fin >> a[i];

    /// prelucrez primele k elemente
      for(i = 1; i <= k; i++)
    {
        x = a[i];
        /// scot din queue toate elementele mai mari
        /// sau egale cu x

        while(!q.empty() && x <= a[q.back()])
            q.pop_back();

       q.push_back(i);

    }
    s += a[q.front()];
    /// restul elementelor
    for(i = k+1; i <= n; i++)
    {
        x = a[i];
        while(!q.empty() && x <= a[q.back()])
            q.pop_back();

        q.push_back(i);

        if(i - q.front() >= k)
            q.pop_front();

       s+=a[q.front()];


    }
    fout << s << "\n";

    return 0;
}