#include <fstream>
#include <deque>
using namespace std;
deque< pair<int,int> > p;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n,k,i,x;
long long v;
int main()
{
    fin>>n>>k;
    for(i=1;i<k;i++)
    {
        fin>>x;
        while(p.size()&&p.back().first>=x)
            p.pop_back();
        p.push_back(make_pair(x,i));
    }
    for(;i<=n;i++)
    {
        fin>>x;
        while(p.size()&&p.back().first>=x)
            p.pop_back();
        p.push_back(make_pair(x,i));
        if(i-p.front().second==k)
            p.pop_front();
        v+=p.front().first;
    }
    fout<<v;
    return 0;
}