#include <fstream>
#include <deque>
#define ind first
#define val second
using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");
deque<pair<int,int>> q;
int n, k, i, v;
long long sol;
int main()
{
    f>>n>>k;
    for(i=1; i<k; i++)
    {
        f>>v;
        while(q.size() && q.back().val >= v)
            q.pop_back();
        q.push_back(make_pair(i,v));
    }
    for(i=k; i<=n; i++)
    {
        f>>v;
        while(q.size() && q.back().val >= v)
            q.pop_back();
        q.push_back(make_pair(i,v));
        if(q.front().ind == i-k)
            q.pop_front();
        sol+=q.front().val;
    }

    g<<sol;

    return 0;
}