#include <fstream>
#include <deque>
using namespace std;

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

int n,k;
long long s;
deque<pair<int,int>>d;

int main()
{
    cin>>n>>k;
    int x;
    for(int i=0;i<k;i++)
    {
        cin>>x;
        while(!d.empty() && d.back().first>=x)
            d.pop_back();
        d.push_back({x,i});
    }
    s+=d.front().first;
    for(int i=k;i<n;i++)
    {
        cin>>x;
        while(!d.empty() && d.back().first>=x)
            d.pop_back();
        d.push_back({x,i});
        while(d.front().second<=i-k)
            d.pop_front();
        s+=d.front().first;
    }
    cout<<s;
    return 0;
}