#include <fstream>
#include <deque>

using namespace std;

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

deque <int>dq;
long long n,i,j,v[5000001],k;
long long rez;

int main()
{

    f>>n>>k;

    for(i=1;i<=k;i++)
        {
            f>>v[i];
            while(!dq.empty()&&v[dq.back()]>=v[i])
                dq.pop_back();
            dq.push_back(i);
        }

    rez=v[dq.front()];
    for(i=k+1;i<=n;i++)
    {
        f>>v[i];
        while(!dq.empty()&&v[dq.back()]>=v[i])
            dq.pop_back();
        dq.push_back(i);
        if(dq.front()<=i-k)
            dq.pop_front();
        rez+=v[dq.front()];
    }

    g<<rez;

    return 0;

}