#include <fstream>
#include <deque>
using namespace std;
int N,K,v[5000001];
long long S;
deque <long long> k;
ifstream f ("deque.in");
ofstream g ("deque.out");
int main()
{
    f>>N>>K;
    for(int i=1;i<=N;i++)
        f>>v[i];
    k.push_back(1);
    for(int i=2;i<=N;i++)
    {
        while(!k.empty() && v[k.back()] > v[i])
            k.pop_back();
        k.push_back(i);
        if(k.front() == i - K)
            k.pop_front();
        if(i >= K)
            S += v[k.front()];
    }
    g<<S;
    f.close();
    g.close();
    return 0;
}