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

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

int a[5000001],q[5000001];
long long s=0;

int main()
{
    int n,k,pq=0,uq=-1,i;
    fin>>n>>k;
    for(i=1;i<k;i++)
    {
        fin>>a[i];
        while(pq<=uq && a[i]<=a[q[uq]])uq--;
        q[++uq]=i;
    }
    for(i=k;i<=n;i++)
    {
        fin>>a[i];
        while(pq<=uq && a[i]<=a[q[uq]])uq--;
        q[++uq]=i;
        if(q[pq]==i-k)pq++;
        s+=a[q[pq]];
    }
    fout<<s;
    return 0;
}