#include <fstream>
#include <deque>

using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");

deque <int> q;

int n, i, k, v[5000010];
long long suma;

int main()
{
    fin>>n>>k;
    for (i=1;i<=n;i++)
    {
        fin>>v[i];
        while (!q.empty()&&v[q.front()]>v[i])q.pop_front();
        q.push_front(i);
        if (i>=k)
        {
            if (q.back()<i-k+1)q.pop_back();
            suma+=v[q.back()];
        }
    }
    fout<<suma;
    return 0;
}