#include<fstream>
#include<deque>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
deque <int> q;
int n,k,a[5000005];
long long s;
int main()
{
    int i;
    fin>>n>>k;
    for (i=1;i<=n;++i)
        fin>>a[i];
    for (i=1;i<=n;++i)
        {
            while (!q.empty() && a[q.back()]>=a[i]) q.pop_back();
            q.push_back(i);
            if (q.front()==i-k) q.pop_front();
            if (i>=k) s+=(long long) a[q.front()];
        }
    fout<<s<<'\n';
    return 0;
}