#include <fstream>
#include <deque>
using namespace std;
ifstream cin ("deque.in");
ofstream cout ("deque.out");
deque <int> v;
int x[5000005];
int main()
{
    long long n,i,j,k,minim,a,suma=0;
    cin>>n>>k;
    for(i=1;i<k;i++)
    {
        cin>>x[i];
        while(!v.empty() && v.back()>x[i])
        {
            v.pop_back();
        }
        v.push_back(x[i]);
    }
    for(i=k;i<=n;i++)
    {
        cin>>x[i];
        while(!v.empty() && v.back()>x[i])
        {
            v.pop_back();
        }
        v.push_back(x[i]);
        a=v.front();
        if(!v.empty() && x[i-k]==v.front())
        {
            v.pop_front();
        }
        suma=suma+v.front();
    }
    cout<<suma;
    return 0;
}