#include <fstream>
#include <deque>
using namespace std;
deque< pair<int,int> > q;
int n,k,i,x;
long long s;
int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    f>>n>>k;
    for(i=1;i<=k-1;i++)
    {
        f>>x;
        while(!q.empty()&&x<q.back().first)
            q.pop_back();
        q.push_back(pair<int,int>(x,i));
    }
    for(i=k;i<=n;i++)
    {
        f>>x;
        while(!q.empty()&&x<q.back().first)
            q.pop_back();
        q.push_back(pair<int,int>(x,i));
        s+=q.front().first;
        if(q.front().second==i-k+1)
            q.pop_front();
    }
    g<<s<<'\n';
    return 0;
}