#include <fstream>
#include <queue>
#define nmax 5000002
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

deque <int> d;
long long v[nmax],sum=0;

int main()
{
    int n,k;
    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)
            sum+=v[d.front()];
    }
    fout<<sum;
    return 0;
}