#include <bits/stdc++.h>

using namespace std;

deque <int> q;
int a[500003], n, k,i, x;
long long s;
int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin >> n >>k;
    for( i =1; i <= n; i++)
        fin >> a[i];

    for(i = 1; i <= k; i++)
    {
        x = a[i];
        while( !q.empty() && x <= a[q.back()])
            q.pop_back();
        q.push_back(i);
    }

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

    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;
    return 0;
}