#include <iostream>
#include <fstream>

using namespace std;

ifstream f("deque.in"); ofstream g("deque.out");
int n, i, k, a[5000005], d[5000005], st, dr;

long long s;

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