#include <bits/stdc++.h>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

const long long nmax = 5000005;
long long n, k, A[nmax];
deque<long long> Dq;

int main()
{
    f >> n >> k;
    for(long long i = 1; i <= n; i ++)f >> A[i];

    for(int i = 1; i <= k; i ++)
    {
        while(!Dq.empty() && A[Dq.back()] > A[i])Dq.pop_back();
        Dq.push_back(i);
    }
    long long sumi = A[Dq.front()];

    for(long long i = k + 1; i <= n; i ++)
    {
        while(!Dq.empty() && Dq.front() + k - 1 < i)Dq.pop_front();
        while(!Dq.empty() && A[Dq.back()] > A[i])Dq.pop_back();
        Dq.push_back(i);
        sumi += A[Dq.front()];
    }

    g << sumi;
    return 0;
}