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

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

deque < int > dq;
long long  ans;
vector < int > v;
int n, k, x;

int main()
{
    fin >> n >> k;
    for (int i=1;i<=n;i++) {
        fin >> x;
        v.push_back(x);
    }

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