#include <bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
long long N, K, A[5000005], i, p, S;
deque<int> Deq;
int main()
{
    f >> N >> K;
    for(i = 1; i <= N; i ++)f >> A[i];

    for(i = 1; i <= N; i ++)
    {
        while(!Deq.empty() && A[Deq.back()] > A[i])
            Deq.pop_back();

        Deq.push_back(i);

        if(i >= K)
        {
            if(i - Deq.front() + 1 > K)Deq.pop_front();
            S += A[Deq.front()];
        }
    }
    g << S;
    return 0;
}