#include <iostream>
#include <fstream>

using namespace std;

int a[5000001],dcoad[5000001];

int main()
{
    ifstream fin ("deque.in");
    ofstream fout ("deque.out");
    int n,k,st,dr;
    long long int sum=0;
    fin>>n>>k;
    for (int i=0; i<n; i++)
        fin>>a[i];
    st=1;
    dr=0;
    for (int i=0; i<n; i++)
    {
        while(st<=dr&&a[i]<=a[dcoad[dr]])dr--;
        dcoad[++dr]=i;
        if(dcoad[st]==i-k)st++;
        if (i>=k-1)sum+=a[dcoad[st]];
    }
    fout<<sum;
    return 0;
}