#include <iostream>
#include <deque>
#include <fstream>

using namespace std;

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

deque <int> D;
int a[5000001];

int main()
{
    int n, k;
    long long s=0;
    fin>>n>>k;
    for(int i=0; i<n; i++)
        fin>>a[i];
    D.push_front(0);
    for(int i=1; i<n; i++)
    {
        if(D.front()==i-k)
            D.pop_front();
        while(!D.empty() && a[i]<a[D.back()])
            D.pop_back();
        D.push_back(i);
        if(i>=k-1)s=s+a[D.front()];
    }
    fout<<s;
    return 0;
}