#include <fstream>
#include<deque>
using namespace std;

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

int v[500005];
deque<int> a;
int n,k;
long long int suma = 0;
int main()
{
    fin>>n>>k;
    for(int i = 1;i <= n;i++)
        fin>>v[i];
    for(int i = 1;i <= n;i++)
    {
        while(!a.empty() && v[i] <= v[a.back()]) a.pop_back();
        a.push_back(i);
        if(a.front() == i - k) a.pop_front();
        if(i >= k) suma = suma + v[a.front()];
    }
    fout<<suma;
    return 0;
}