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