#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

deque <int> dq;
int n,k,a[5000001],i;
long long s;

void citire()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++)
        fin>>a[i];
}

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