#include <bits/stdc++.h>
#define nmax 5000001
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int a[nmax],n,k;
deque<int>q;
void Citire()
{
    int i;
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>a[i];
}
void Rezolvare()
{
    int i,x;
    long long sol=0;
    for(i=1;i<=k;i++)
    {
        x=a[i];
        while(!q.empty() && a[q.back()]>x)
            q.pop_back();
        q.push_back(i);
    }
    sol+=a[q.front()];
    for(i=k+1;i<=n;i++)
    {
        x=a[i];
        while(!q.empty() && a[q.back()]>x)
            q.pop_back();
        q.push_back(i);
        if(i-q.front()>=k)
            q.pop_front();
        sol+=a[q.front()];
    }
    fout<<sol<<"\n";
}
int main()
{
    Citire();
    Rezolvare();
    fin.close();
    fout.close();
    return 0;
}