#include <fstream>
#include <deque>

int v[5000000];

using namespace std;

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

int main()
{
    int n,i,s=0,k;

    deque <int> dq;

    fin >>n>> k;

    for(i=0;i<n;i++){
        fin >> v[i];
    }

    for(i=0;i<n;i++){
        while(!dq.empty()&&v[i]<v[dq.back()]){
            dq.pop_back();
        }
        dq.push_back(i);
        if(!dq.empty()&&dq.front() == i-k){
            dq.pop_front();
        }

        if(i>=k-1)
            s+=v[dq.front()];
    }
    fout << s;
    return 0;
}