#include <bits/stdc++.h>

#define NMax 5000005

using namespace std;

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



int N,K;
int x[NMax];
long long sum;
deque<int> Deque;

int main()
{
    fin>>N>>K;
    for(int i=1;i<=N;i++)
        fin>>x[i];

    for(int i=1;i<=N;i++)
    {
        if(!Deque.empty())
        {
            while(!Deque.empty() && x[Deque.back()]>=x[i])
                Deque.pop_back();

            if(!Deque.empty() && Deque.front()<=i-K)
                Deque.pop_front();
        }
        Deque.push_back(i);
        if(i>=K)
            sum+=x[Deque.front()];
    }
    fout<<sum;

    return 0;
}