#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
deque< pair<int,int> > q;
int a,n,k;
long long s;
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(NULL);
    cin>>n>>k;
    for(int i=0;i<n;++i)
    {
        cin>>a;
        while(!q.empty()&&a<q.back().first) q.pop_back();
        q.push_back(make_pair(a,i));
        if(i-q.front().second==k) q.pop_front();
        if(i>=k-1) s+=q.front().first;
    }
    cout<<s<<"\n";
    return 0;
}