#include <fstream>
#include <deque>

using namespace std;

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

deque <int> d;
int v[5000001];

int main()
{
    int n,k,i;
    long long s=0;
    cin>>n>>k;
    for(i=1;i<=n;i++)
    {
        cin>>v[i];
        while(!d.empty() && v[i]<v[d.back()])
            d.pop_back();
        d.push_back(i);
        if(i>=k)
        {
            s=s+v[d.front()];
            if(!d.empty() && d.front()+k-1<=i)
                d.pop_front();
        }

    }

    cout<<s;
    return 0;
}