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

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

deque <int> d;
int v[5000010];
int main()
{
    int n, k;
    fin>>n>>k;
    int i, j=1;
    long long suma=0;
    for(i=1; i<=n; i++)
    {
        fin>>v[i];
        if(i - d.front() >= k) //imi pastrez secventa de k elem
            d.pop_front();
        while( (v[i] <= v[d.back()]) && d.size()) //pastram elem minime
            d.pop_back();
        d.push_back(i); //adaugam elem mic
        if( i - j == k-1 )
        {
            suma += v[d.front()]; //primul elem e minim
            j++;
        }
    }
    fout<<suma;

}