#include <iostream> #include <cmath> using std::cin; using std::cout; const char endl = '\n'; const int N = 3e5 + 5; struct node { int l, r; long long s, d; node() : l(0), r(0), s(0), d(0) {} node(int _l, int _r) : l(_l), r(_r), s(0), d(0) {} } tr[N << 2]; int n, k; long long x, t, ans, a[N], b[N]; bool flag[N]; inline void pushup(int u) { tr[u].s = tr[u << 1].s + tr[u << 1 | 1].s; } inline void pushdown(int u) { tr[u << 1].s += (tr[u << 1].r - tr[u << 1].l + 1) * tr[u].d; tr[u << 1].d += tr[u].d; tr[u << 1 | 1].s += (tr[u << 1 | 1].r - tr[u << 1 | 1].l + 1) * tr[u].d; tr[u << 1 | 1].d += tr[u].d; tr[u].d = 0; } void build(int u, int l, int r) { tr[u] = node(l, r); if (l == r) { tr[u].s = b[l]; return; } int mid = l + r >> 1; build(u << 1, l, mid); build(u << 1 | 1, mid + 1, r); pushup(u); } void modify(int u, int l, int r, long long d) { if (l <= tr[u].l && tr[u].r <= r) { tr[u].s += (tr[u].r - tr[u].l + 1) * d; tr[u].d += d; return; } pushdown(u); int mid = tr[u].l + tr[u].r >> 1; if (l <= mid) modify(u << 1, l, r, d); if (r > mid) modify(u << 1 | 1, l, r, d); pushup(u); } long long query(int u, int l, int r) { if (l <= tr[u].l && tr[u].r <= r) { return tr[u].s; } pushdown(u); int mid = tr[u].l + tr[u].r >> 1; long long sum = 0; if (l <= mid) sum += query(u << 1, l, r); if (r > mid) sum += query(u << 1 | 1, l, r); return sum; } int main() { std::ios::sync_with_stdio(false); cin >> n >> k; for (int i = 1; i <= n; i++) { cin >> a[i]; b[i] = a[i] - a[i - 1]; } build(1, 1, n); for (int i = n; i >= k; i--) { if ((t = query(1, 1, i)) > 0) { x = std::ceil(1.0 * t / k); modify(1, i - k + 1, i, -x); ans += x; } } t = 0; for (int i = 1; i < k; i++) { t = std::max(t, (long long)ceil(1.0 * query(1, 1, i) / i)); } cout << ans + t << endl; return 0; }