#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
deque<int> D;
int A[5000001];
int n,k;
long long S;
int main()
{
    ifstream f("deque.in");
    f>>n>>k;
    for(int i=1;i<=n;i++)
    {
        f>>A[i];
        while(!D.empty()&&A[i]<=A[D.back()])D.pop_back();
        D.push_back(i);
        if(A[D.front()]==i-k) D.pop_front();
        if(i>=k)S+=A[D.front()];
    }
    f.close();
    ofstream g("deque.out");
    g<<S;
    g.close();
    return 0;
}