#include <fstream>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int a[5000005], dq[5000005], st, dr, i,n,k;
long long s;

int main() {
    f >> n >> k;
    st=1;
    for (i = 1; i <= n; i++) {
        f >> a[i];
        while (st<=dr && a[i] <= a[dq[dr]])
            dr--;
        dq[++dr] = i;
        if (dq[st] == i-k)
            st++;
        if (i>=k)
            s += a[dq[st]];
    }
    g << s;
    return 0;
}