#include <bits/stdc++.h>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <int> d;
vector <int> v;
int main()
{
    int n,k;
    fin>>n>>k;
    for(int i=1; i<=n; i++)
    {
        int a;
        fin>>a;
        v.push_back(a);
    }
    int sum=0;
    for(int i=0; i<n; i++)
    {
        int a=v[i];
        while(!d.empty()&&a<=v[d.back()])
        {
            d.pop_back();
        }
        d.push_back(i);
        if(i>=k&&d.front()<=i-k)
            d.pop_front();
        if(i>=k-1)
            sum+=v[d.front()];
    }
    fout<<sum;
    return 0;
}