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

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

const int nmax=5000000;
int v[nmax];
int main()
{
    int n,aux,i,s=0;
    deque <int> d;
    in>>n>>aux;

    for(i=0; i<n; i++)
    {

        in>>v[i];

        while(!d.empty() && v[i] < v[d.back()])
            d.pop_back();

        d.push_back(i);
        if( d.front() <= i - aux) d.pop_front();
        if ( i >= aux - 1 ) s+=v[d.front()];

    }
    out<<s;

    return 0;
}