#include <bits/stdc++.h>
using namespace std;
const long double PI = acos(-1);
const long double eps = 0.0000000001;
const long long INF = 0x3fffffffffffffff;
long long a[200005], sum[200005], n, q, x, y;
long long lowbit(long long now) { return now & -now; }
void add(long long pos, long long v) {
  while (pos <= n) {
    sum[pos] += v;
    pos += lowbit(pos);
  }
}
long long query(long long now) {
  long long res = 0;
  while (now) {
    res += sum[now];
    now ^= lowbit(now);
  }
  return res;
}
long long findnext(long long now) {
  long long l = now + 1, r = n + 1, v = query(now);
  while (l < r) {
    long long mid = (l + r) >> 1;
    if (query(mid) < v << 1) {
      l = mid + 1;
    } else {
      r = mid;
    }
  }
  return l;
}
signed main() {
  ios::sync_with_stdio(false);
  cin >> n >> q;
  for (long long i = 1; i <= n; ++i) {
    cin >> a[i];
    add(i, a[i]);
  }
  for (long long i = 1; i <= q; ++i) {
    cin >> x >> y;
    add(x, -a[x]);
    a[x] = y;
    add(x, a[x]);
    long long now = 1;
    bool flag = false;
    if (a[1] == 0) {
      cout << 1 << endl;
      continue;
    }
    while (now <= n) {
      now = findnext(now);
      if (now <= n && query(now) == a[now] << 1) {
        cout << now << endl;
        flag = true;
        break;
      }
    }
    if (!flag) {
      cout << -1 << endl;
    }
  }
  return 0;
}
