import sys input = sys.stdin.readline class LazySegmentTree: def __init__( self, n, identity_e_node, identity_e_lazy, combine_node_f, combine_lazy_f, reflect_f, ): self._n = n self._size = 1 self._height = 0 while self._size < self._n: self._size <<= 1 self._height += 1 self._identity_e_node = identity_e_node self._identity_e_lazy = identity_e_lazy self._combine_node_f = combine_node_f self._combine_lazy_f = combine_lazy_f self._reflect_f = reflect_f self._node = [self._identity_e_node] * (2 * self._size) self._lazy = [self._identity_e_lazy] * (2 * self._size) #遅延データの値を値データに反映させたときの値を返す。 def _reflect_lazy(self, index): return self._reflect_f(self._node[index], self._lazy[index]) def _propagate_from_top(self, index): index += self._size for h in range(self._height, 0, -1): i = index >> h if self._lazy[i] != self._identity_e_lazy: self._lazy[i << 1] = self._combine_lazy_f( self._lazy[i << 1], self._lazy[i] ) self._lazy[i << 1 | 1] = self._combine_lazy_f( self._lazy[i << 1 | 1], self._lazy[i] ) self._node[i] = self._reflect_lazy(i) self._lazy[i] = self._identity_e_lazy def _update_from_bottom(self, index): index = (index + self._size) >> 1 while index: self._node[index] = self._combine_node_f( self._reflect_lazy(index << 1), self._reflect_lazy(index << 1 | 1) ) index >>= 1 def build(self, array): assert len(array) == self._n for index, value in enumerate(array, start=self._size): self._node[index] = value for index in range(self._size - 1, 0, -1): self._node[index] = self._combine_node_f( self._node[index << 1], self._node[index << 1 | 1] ) # 区間更新 位置[L, R) (0-indexed)を値valueで更新 def update(self, L, R, value): self._propagate_from_top(L) self._propagate_from_top(R - 1) L_lazy = L + self._size R_lazy = R + self._size while L_lazy < R_lazy: if L_lazy & 1: self._lazy[L_lazy] = self._combine_lazy_f(self._lazy[L_lazy], value) L_lazy += 1 if R_lazy & 1: R_lazy -= 1 self._lazy[R_lazy] = self._combine_lazy_f(self._lazy[R_lazy], value) L_lazy >>= 1 R_lazy >>= 1 self._update_from_bottom(L) self._update_from_bottom(R - 1) # 区間取得 区間[L, R) (0-indexed)内の要素について # L番目から順にcombine_node_fを適用した値を返す。 def fold(self, L, R): self._propagate_from_top(L) self._propagate_from_top(R - 1) L += self._size R += self._size value_L = self._identity_e_node value_R = self._identity_e_node while L < R: if L & 1: value_L = self._combine_node_f(value_L, self._reflect_lazy(L)) L += 1 if R & 1: R -= 1 value_R = self._combine_node_f(self._reflect_lazy(R), value_R) L >>= 1 R >>= 1 return self._combine_node_f(value_L, value_R) def op(x1, x2): v1, s1 = x1 v2, s2 = x2 return (v1 + v2, s1 + s2) def reflect_f(node, lazy): return (node[0] + lazy * node[1], node[1]) N, M = map(int, input().split()) A = list(map(int, input().split())) X, W = [0] * M, [0] * M for i in range(M): X[i], W[i] = map(int, input().split()) X[i] -= 1 from operator import add def f(l, vl, r, vr, c, T): T.update(l+1, r+1, c) T.update(l, l + 1, vl) T.update(r+1, r + 2, -vr) return T def printT(T): ans = [] for i in range(N): ans.append(T.fold(0, i + 1)[0]) print("test", *ans) def check(m): T = LazySegmentTree(N+1, (0, 0), 0, op, add, reflect_f) T.build([(0, 1) for _ in range(N + 1)]) for x, w in zip(X, W): d = w // m r = min(x + d, N - 1) v = w - (r - x) * m T = f(x, w, r, v, -m, T) # printT(T) l = max(0, x - d) v = w - (x - l) * m T = f(l, v, x, w, m, T) T.update(x, x + 1, -w) T.update(x+1, x+2, w) # printT(T) for i in range(N): v = T.fold(0, i + 1)[0] if v >= A[i]: return False return True sw = sum(W) flag = 1 for i in range(N): if A[i] <= sw: flag = 0 if flag: print(0) exit() yes = 10 ** 9 + 5 no = 0 if not check(yes): print(-1) exit() while yes - no != 1: mid = (yes + no)//2 if check(mid): yes = mid else: no = mid print(yes)