#include <fstream>
#include <deque>

using namespace std;

ifstream f("in.in");
ofstream g("in.out");

int N,K,i;
int a[5000005];
long long  S;

int main()
{
    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;

}