#include <fstream>
#include <deque>
#define sz 5000000
using namespace std;

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

int n,k;
deque <pair<int,int>> q;
long long sol;
int x;

int main()
{
    fin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        fin>>x;
        while(q.empty()==false && q.front().first <= i-k)
            q.pop_front();
        while(q.empty()==false && x <= q.back().second)
            q.pop_back();
        q.push_back({i,x});
        if(i>=k)
            sol+=q.front().second;
    }
    fout<<sol;
}