#include <bits/stdc++.h>
#define NMAX  5e6+ 1

using namespace std;

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

int a[NMAX];

int main()
{
    int n, k;
    fin>>n>>k;
    for(int i=1; i<=n; ++i)
        fin>>a[i];

    deque<int> dq;
    for(int i=1; i<=k; ++i)
    {
        while(!dq.empty() && a[dq.back()]>=a[i])
            dq.pop_back();
        dq.push_back(i);
    }
    long long sum=a[dq.front()];

    for(int i=k+1; i<=n; ++i)
    {
        int left=i-k+1;
        while(!dq.empty() && a[dq.back()]>=a[i])
            dq.pop_back();
        if(!dq.empty() && dq.front()<left)
            dq.pop_front();
        dq.push_back(i);
        sum+=a[dq.front()];
    }
    fout<<sum<<'\n';
    return 0;
}