#include <fstream>
#include<deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,i,x[5000001],k;
long long s;
deque< int> dq;
int main()
{
    fin>>n>>k;
    for(i=1;i<=k;i++)
    {
        fin>>x[i];
        while(!dq.empty()&&x[i]<=x[dq.back()])
        {
            dq.pop_back();
        }
        dq.push_back(i);

    }
    s=x[dq.front()];
    for(i=k+1;i<=n;i++)
    {
        fin>>x[i];
        while(!dq.empty()&&x[i]<=x[dq.back()])
            dq.pop_back();
        dq.push_back(i);

        if(dq.front()<=i-k)
        {
            dq.pop_front();
        }
        s+=x[dq.front()];
    }
    fout<<s;
    return 0;
}