#include<deque>
#include<fstream>
using namespace std;
#define FIN "deque.in"
#define FOUT "deque.out"
#define MAXN 5000001

ifstream f(FIN);
ofstream g(FOUT);

deque<int> d;
int v[MAXN];
int n, k;

int main()
{
    f >> n;
    f >> k;

    long int sum = 0;

    for(int i=1; i<=n; i++)
        f >> v[i];

    for(int i=1; i<=n; i++)
    {

        if(d.size() > 0)
        {
            while(v[d.back()] >= v[i])
            {
                d.pop_back();
                if(d.size() == 0)
                    break;
            }

        }

        d.push_back(i);

        if(i > k)
        {
            if(i-k >= d.front())
                d.pop_front();
        }

        if( i >= k)
            sum += v[d.front()];
    }

    g << sum;

    return 0;

}