#include <fstream>
#include <deque>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");
int main()
{
    int N,K,i,a[5000000];
    long long S;
    deque <int> h;

    f>>N>>K;
    S=0;
    for(i=1;i<=N;i++)
    {
        f>>a[i];
        while(h.size() && a[h.back()]>=a[i]) h.pop_back();
        h.push_back(i);
        if(i>=K) S+=a[h.front()];
        if(h.front()<=(i-K+1))
                     h.pop_front();
    }
    g<<S;
    return 0;

}