#include <bits/stdc++.h>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <int> q;
int v[5000001];
int main()
{
    int n,k;
    fin>>n>>k;
    long long sum=0;
    for(int i=1;i<=n;i++)
    {
        fin>>v[i];
        while(!q.empty() && v[i]<=v[q.back()])
            q.pop_back();
        q.push_back(i);
        if(i-q.front()+1>k)
            q.pop_front();
        if(i>=k)
        {
            sum+=v[q.front()];
        }
    }
    fout<<sum;
    return 0;
}