#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

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

int v[5000001];

deque <int> min_dq;

int main()
{

    int n,i,k;
    f>>n>>k;
    for(i=1;i<=n;i++)
        f>>v[i];

    long long sum=0;

    for(i=1;i<=k;i++)
    {
        while(!min_dq.empty() and v[min_dq.back()]>v[i])
            min_dq.pop_back();
        min_dq.push_back(i);
    }

    sum+=v[min_dq.front()];

    for(i=k+1;i<=n;i++)
    {
        if(!min_dq.empty() and min_dq.front()<=i-k)
            min_dq.pop_front();


        while(!min_dq.empty() and v[min_dq.back()]>v[i])
            min_dq.pop_back();
        min_dq.push_back(i);

        sum+=v[min_dq.front()];
    }

    g<<sum;

    return 0;
}