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

using namespace std;

deque<int> d;
int n,k;
const int NMAX = 5000001;
ifstream in("deque.in");
ofstream out("deque.out");
int a[NMAX];
long long int s = 0;

int main()
{
    in>>n>>k;
    for(int i=1;i<=n;i++)
        in>>a[i];
    in.close();
    for(int i=1;i<=n;i++)
    {
        while(!d.empty() && a[d.back()] > a[i])
            d.pop_back();
          d.push_back(i);
        if(!d.empty() && d.front() == i-k)
            d.pop_front();
        if(i>=k)
            s+=a[d.front()];
    }
    out<<s<<"\n";
    out.close();
    return 0;
}