#include <fstream>
#include <deque>l
using namespace std;

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

long long s,i,j,n,k;
long int A[5000010];
deque <int> dq;

int main()
{
    fin>>n;
    fin>>k;
    for(i=1;i<=n;i++)
        fin>>A[i];

    for(i=1;i<=n;i++)
    {
        if(!dq.empty() && dq.front()==i-k)
            dq.pop_front();
        while(!dq.empty()&& A[dq.back()]>A[i])
            dq.pop_back();
        dq.push_back(i);
        if(i>=k) s+=A[dq.front()];
    }
fout<<s;
}