#include <fstream>
#include <deque>
#include <vector>

using namespace std;

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

const int N=5e6+2;

int v[N];

deque <int> dq;

int main()
{
    int n,k;
    long long ans=0;
    in>>n>>k;
    for(int i=0;i<n;++i)
    {
        in>>v[i];
    }
    for(int i=0;i<n;++i)
    {
        if(dq.front()==i-k)
        {
            dq.pop_front();
        }
        while(!dq.empty() && v[i]<=v[dq.back()])
        {
            dq.pop_back();
        }
        dq.push_back(i);
        if(i>=k-1)
        {
            ans+=v[dq.front()];
        }
    }
    out<<ans;
    return 0;
}