#include <bits/stdc++.h>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <int> q;
int a[5000003];
int main()
{
    int i,n,k,x;
    fin>>n>>k;
    long long sum=0;
    for(i=1;i<=n;i++)
        fin>>a[i];
    for(i=1;i<=k;i++)
    {
        x=a[i];
        while(!q.empty()&&x<=a[q.back()]) q.pop_back();
        q.push_back(i);
    }
    sum+=a[q.front()];
    for(i=k+1;i<=n;i++)
    {
        x=a[i];
        while(!q.empty()&&x<=a[q.back()]) q.pop_back();
        q.push_back(i);
        if(i-q.front()>=k)
            q.pop_front();
        sum+=a[q.front()];
    }
    fout<<sum<<"\n";
    fout.close();
    return 0;
}