#include <fstream>

int d[5000000], st = 0, dr = -1, v[5000000];

int main() {
    std::ifstream in("deque.in");
    std::ofstream out("deque.out");

    int n, k;
    in >> n >> k;

    long long s = 0;
    for (int i = 0; i < n; ++i) {
        in >> v[i];
        if (st <= dr && d[st] == i - k) ++st;
        while (st <= dr && v[i] <= v[d[dr]]) --dr;
        d[++dr] = i;
        if (i >= k - 1) s += v[d[st]];
    }

    out << s;

    return 0;
}