#include <bits/stdc++.h>

#define NMax 5000005

using namespace std;

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

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

int main()
{
    fin>>N>>K;
    for(int i=1;i<=N;i++)
        fin>>A[i];
    for(int i=1;i<=N;i++)
    {
        while(!Deque.empty() && Deque.front()<i-K+1)
            Deque.pop_front();
        while(!Deque.empty() && A[Deque.back()]>A[i])
            Deque.pop_back();
        Deque.push_back(i);
        if(i>=K)
            sum+=A[Deque.front()];
    }
    fout<<sum;

    return 0;
}