#include <fstream>
#include <deque>
using namespace std;
int v[5000005];
deque<int>q;
int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int n,k,poz=0;
    long long sum=0;
    fin>>n>>k;
    for(int i=1;i<=k;i++)
    {
        fin>>v[i];
        while(!q.empty()&&v[q.back()]>v[i])
        {
            q.pop_back();
        }
        q.push_back(i);
    }
    sum+=v[q.front()];
    for(int i=k+1;i<=n;i++)
    {
        if(v[q.front()]==v[i-k])
        {
            q.pop_front();
        }
        fin>>v[i];
         while(!q.empty()&&v[q.back()]>v[i])
        {
            q.pop_back();
        }
        q.push_back(i);
        sum+=v[q.front()];
    }
    fout<<sum<<'\n';
    return 0;
}