#include <fstream>

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

int dq[500002], a[500002];
int i, st,dr, n, k;
long long su;

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