#include <fstream>
#include <queue>
#define maxn 5000010
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int v[maxn];

int main()
{
    int n, k;
    in >>n >>k;
    long long s = 0;
    deque <int> dq;
    for (int i = 1; i <= n; i++)
    {
        in >>v[i];
        while(!dq.empty() && v[i] <= v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if (dq.front() == i-k)
            dq.pop_front();
        if (i >= k)
            s += v[ dq.front()];
    }
    out<<s;
    return 0;
}