#include <fstream>
#include <deque>

using namespace std;

ifstream fin ("deque.in");
ofstream cout("deque.out");

deque<int> q;
int a[5000005];

int main()
{
    int n, k, x;
    long long s = 0;
    fin >> n >> k;
    for(int i = 1; i <= n; ++i) fin >> a[i];
    ///prelucrez primele k elemente
    for(int i = 1; i <= k; ++i)
    {
         x = a[i];
        /// scot din queue toate elem >= cu x;
        while(!q.empty() && x <= a[q.back()])
            q.pop_back();
        q.push_back(i);
    }
    s += a[q.front()];
    for(int i = k + 1; i <= n; ++i)
    {
        x = a[i];

        while(!q.empty() && x <= a[q.back()])
            q.pop_back();
        q.push_back(i);
        /// verific daca s-a invechit un elem
        if(i-q.front() >= k) q.pop_front();
        s += a[q.front()];
    }
    cout << s;
    return 0;
}