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

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

deque < int > dq;
//unsigned long long
long long int n, k, v[5000001], s;
int main()
{
    cin>>n>>k;
    for(int i=0; i<n; i++)
    {
        cin>>v[i];
    }
    for(int i=0;i<k; i++)
    {
        while(!dq.empty() && dq.back()>v[i])
        {
            dq.pop_back();
        }
        dq.push_back(v[i]);
    }
    s+=1LL*dq.front();
    for(int i=0; i<n-k; i++)
    {
        if(!dq.empty() && dq.front()==v[i])
        {
            dq.pop_front();
        }
        int next=v[i+k];
        while(!dq.empty() && dq.back()>next)
        {
            dq.pop_back();
        }
        dq.push_back(next);
        s=s+1LL*dq.front();
    }
    cout<<s;
    return 0;
}