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