#include <bits/stdc++.h>
using namespace std;
vector<long long> rmq_sum;
vector<int> v, rmq_max;
int n;
void create(int i, int l, int r) {
  if (r - l == 1) {
    rmq_sum[i] = v[l], rmq_max[i] = v[l];
    return;
  }
  int mid = (l + r) / 2;
  create(2 * i + 1, l, mid);
  create(2 * i + 2, mid, r);
  rmq_sum[i] = rmq_sum[2 * i + 1] + rmq_sum[2 * i + 2];
  rmq_max[i] = max(rmq_max[2 * i + 1], rmq_max[2 * i + 2]);
}
void change(int i, int l, int r, int ind, int num) {
  if (r - l == 1) {
    rmq_sum[i] = num, rmq_max[i] = num;
    return;
  }
  int mid = (l + r) / 2;
  if (ind < mid)
    change(2 * i + 1, l, mid, ind, num);
  else
    change(2 * i + 2, mid, r, ind, num);
  rmq_sum[i] = rmq_sum[2 * i + 1] + rmq_sum[2 * i + 2];
  rmq_max[i] = max(rmq_max[2 * i + 1], rmq_max[2 * i + 2]);
}
int down(int i, int l, int r, long long S) {
  if (r - l == 1) return l;
  int mid = (l + r) / 2;
  if ((long long)rmq_max[2 * i + 1] >= S) return down(2 * i + 1, l, mid, S);
  return down(2 * i + 2, mid, r, S);
}
int get(int i, int l, int r, int l1, int r1, long long S) {
  if (l1 >= r1) return n;
  if (l == l1 && r == r1) {
    if ((long long)rmq_max[i] < S) return n;
    return down(i, l, r, S);
  }
  int mid = (l + r) / 2;
  int res = get(2 * i + 1, l, mid, l1, min(r1, mid), S);
  if (res != n) return res;
  return get(2 * i + 2, mid, r, max(l1, mid), r1, S);
}
long long get_sum(int i, int l, int r, int l1, int r1) {
  if (l1 >= r1) return 0;
  if (l == l1 && r == r1) return rmq_sum[i];
  int mid = (l + r) / 2;
  return get_sum(2 * i + 1, l, mid, l1, min(r1, mid)) +
         get_sum(2 * i + 2, mid, r, max(l1, mid), r1);
}
pair<long long, bool> check(int ind) {
  long long a = get_sum(0, 0, n, 0, ind);
  long long b = get_sum(0, 0, n, ind, ind + 1);
  return {a + b, (a == b)};
}
int ask() {
  int ind = 0;
  long long sum = 0;
  while (ind < n) {
    int new_ind = get(0, 0, n, ind, n, sum);
    if (new_ind == n) break;
    pair<long long, bool> p = check(new_ind);
    if (p.second) return new_ind + 1;
    ind = new_ind + 1;
    sum = p.first;
  }
  return -1;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int q;
  cin >> n >> q;
  for (int i = 0; i < n; i++) {
    int x;
    cin >> x;
    v.push_back(x);
  }
  for (int i = 0; i < 4 * n; i++) {
    rmq_sum.push_back(0);
    rmq_max.push_back(0);
  }
  create(0, 0, n);
  for (int i = 0; i < q; i++) {
    int ind, num;
    cin >> ind >> num;
    change(0, 0, n, ind - 1, num);
    cout << ask() << endl;
  }
}
