#include <bits/stdc++.h>

using namespace std;
int n,k,x,ans;
ifstream fin("date.in");
ofstream fout("date.out");
deque <int> deq;
vector <int> v;

void citire()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        fin>>x;
        v.push_back(x);
    }
}

int main()
{
    citire();

    for(int i=0;i<n-1;i++)
    {
        while(!deq.empty() && v[deq.back()]>v[i])
            deq.pop_back();
        deq.push_back(i);
    }
    for(int i=k-1; i<=v.size();i++)
    {

        if(i-deq.front()== k)
            deq.pop_front();
        while(!deq.empty() && v[deq.back()]>v[i])
            deq.pop_back();
        deq.push_back(i);
        ans+=v[deq.front()];
    }
    fout<<ans;
    return 0;
}