#include <fstream>
#include <deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <int> dq;
int n,k,v[5000001];
long long s;
int main()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++)
    {   fin>>v[i];
        if(!dq.empty()&&v[i]<v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if(i-dq.front()>=k)
            dq.pop_front();
        if(i>=k)
            s+=v[dq.front()];
    }
    fout<<s;
    return 0;
}