#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque<pair<int,int>>q;
int n,k;
long long suma=0;
int main()
{
    f>>n>>k;
    for(int i=1; i<=n; i++)
    {
        int x;
        f>>x;
        while(q.size() and q.front().second+k<=i)
            q.pop_front();
        while(q.size() and q.back().first>x)
        {
            q.pop_back();
        }
        q.push_back({x,i});
        if(i>=k)
            suma+=q.front().first;
    }
    g<<suma;
    return 0;
}