#include <fstream>
#include <deque>

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


deque < pair < int , int > > dq;
int main()
{
    int n,k,a;
    long long s=0;
    cin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        cin>>a;
        if(!dq.empty()&&dq.front().second==i-k)
            dq.pop_front();
        while(!dq.empty()&&a<=dq.back().first)
            dq.pop_back();
        dq.push_back({a,i});
        if(i>=k)
            s+=dq.front().first;
    }
    cout<<s;
    return 0;
}