#include <fstream>

using namespace std;

const int N = 5e6;

int v[N], dq[N+1];

int main(){
    ifstream in("deque.in");
    ofstream out("deque.out");
    int n, k, st, dr;
    long long s = 0;
    in>>n>>k;
    st = 1, dr = 0;
    for(int i=0;i < n; ++i) {
        in >> v[i];
        if (st <=dr && dq[st] == i - k)
            ++st;
        while (st <=dr && v[i] <=v[dq[dr]])
            dr--;
        dq[++dr] = i;
        if (i >= k - 1)
            s +=v[dq[st]];
    }
    out<<s;

    in.close();
    out.close();
    return 0;
}