package main

import (
	"database/sql"
)

type segmentTree struct {
	N   int
	seg []int
}

// Build segment tree
func (s segmentTree) build(a *sql.Rows, l, r, n int) {
	if l == r {
		a.Next()
		a.Scan(&s.seg[n])
		return
	}
	m := (l + r) >> 1
	s.build(a, l, m, n<<1)
	s.build(a, m+1, r, n<<1|1)
	s.seg[n] = s.seg[n<<1] + s.seg[n<<1|1]
}

// Update value at index x
func (s segmentTree) update(x, v, l, r, n int) {
	if l == r {
		s.seg[n] = v
		return
	}
	m := (l + r) >> 1
	if x <= m {
		s.update(x, v, l, m, n<<1)
	} else {
		s.update(x, v, m+1, r, n<<1|1)
	}
	s.seg[n] = s.seg[n<<1] + s.seg[n<<1|1]
}

// Find element with prefix sum v
func (s segmentTree) query(v, l, r, n int) (int, int) {
	if l == r {
		return s.seg[n], l
	}
	m := (l + r) >> 1
	if s.seg[n<<1] >= v {
		return s.query(v, l, m, n<<1)
	} else {
		return s.query(v-s.seg[n<<1], m+1, r, n<<1|1)
	}
}