#include <bits/stdc++.h>
#pragma GCC target("avx2")
#pragma GCC optimization("O3")
#pragma GCC optimization("unroll-loops")
using namespace std;
template <class T1, class T2>
inline bool chmax(T1 &a, T2 b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T1, class T2>
inline bool chmin(T1 &a, T2 b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
const double EPS = 1e-9, PI = acos(-1);
const double pi = 3.141592653589793238462643383279;
template <int mod>
struct ModInt {
  int x;
  ModInt() : x(0) {}
  ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {}
  ModInt &operator+=(const ModInt &p) {
    if ((x += p.x) >= mod) x -= mod;
    return *this;
  }
  ModInt &operator-=(const ModInt &p) {
    if ((x += mod - p.x) >= mod) x -= mod;
    return *this;
  }
  ModInt &operator*=(const ModInt &p) {
    x = (int)(1LL * x * p.x % mod);
    return *this;
  }
  ModInt &operator/=(const ModInt &p) {
    *this *= p.inverse();
    return *this;
  }
  ModInt operator-() const { return ModInt(-x); }
  ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; }
  ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; }
  ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; }
  ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; }
  bool operator==(const ModInt &p) const { return x == p.x; }
  bool operator!=(const ModInt &p) const { return x != p.x; }
  ModInt inverse() const {
    int a = x, b = mod, u = 1, v = 0, t;
    while (b > 0) {
      t = a / b;
      swap(a -= t * b, b);
      swap(u -= t * v, v);
    }
    return ModInt(u);
  }
  ModInt pow(int64_t n) const {
    ModInt ret(1), mul(x);
    while (n > 0) {
      if (n & 1) ret *= mul;
      mul *= mul;
      n >>= 1;
    }
    return ret;
  }
  friend ostream &operator<<(ostream &os, const ModInt &p) { return os << p.x; }
  friend istream &operator>>(istream &is, ModInt &a) {
    int64_t t;
    is >> t;
    a = ModInt<mod>(t);
    return (is);
  }
  static int get_mod() { return mod; }
};
using modint = ModInt<998244353>;
template <typename T>
struct Combination {
  vector<T> _fact, _rfact, _inv;
  Combination(int sz) : _fact(sz + 1), _rfact(sz + 1), _inv(sz + 1) {
    _fact[0] = _rfact[sz] = _inv[0] = 1;
    for (int i = 1; i <= sz; i++) _fact[i] = _fact[i - 1] * i;
    _rfact[sz] /= _fact[sz];
    for (int i = sz - 1; i >= 0; i--) _rfact[i] = _rfact[i + 1] * (i + 1);
    for (int i = 1; i <= sz; i++) _inv[i] = _rfact[i] * _fact[i - 1];
  }
  inline T fact(int k) const { return _fact[k]; }
  inline T rfact(int k) const { return _rfact[k]; }
  inline T inv(int k) const { return _inv[k]; }
  T P(int n, int r) const {
    if (r < 0 || n < r) return 0;
    return fact(n) * rfact(n - r);
  }
  T C(int p, int q) const {
    if (q < 0 || p < q) return 0;
    return fact(p) * rfact(q) * rfact(p - q);
  }
  T H(int n, int r) const {
    if (n < 0 || r < 0) return (0);
    return r == 0 ? 1 : C(n + r - 1, r);
  }
};
long long GCD(long long a, long long b) { return (b == 0) ? a : GCD(b, a % b); }
long long LCM(long long a, long long b) { return a / GCD(a, b) * b; }
template <typename T = int>
struct BIT {
  vector<T> node;
  int N;
  BIT(int n) {
    N = n;
    node.resize(N + 1);
  }
  void add(int i, T x) {
    i++;
    while (i <= N) {
      node[i] += x;
      i += (i & -i);
    }
  }
  T sum(int i) {
    T res = 0;
    i++;
    while (i > 0) {
      res += node[i];
      i -= (i & -i);
    }
    return res;
  }
  long long query(int i, int j) { return sum(j) - sum(i - 1); }
};
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(12);
  int n, q;
  cin >> n >> q;
  BIT<long long> bit(n);
  for (int i = 0; i < (int)n; ++i) {
    long long a;
    cin >> a;
    bit.add(i, a);
  }
  while (q--) {
    {
      int p, x;
      cin >> p >> x;
      p--;
      long long sa = x - bit.query(p, p);
      bit.add(p, sa);
    }
    int ans = -1;
    if (bit.query(0, 0) == 0)
      ans = 1;
    else {
      for (int i = 1; i < n; i++) {
        long long sum = max(1LL, bit.sum(i - 1));
        int lo = i, hi = n;
        while (hi - lo > 1) {
          int mid = (lo + hi) / 2;
          if (bit.sum(mid) < sum * 2)
            lo = mid + 1;
          else
            hi = mid;
        }
        i = lo;
        if (i < n && bit.sum(lo) == bit.sum(lo - 1) * 2) {
          ans = lo + 1;
          break;
        }
      }
    }
    cout << ans << '\n';
  }
  return 0;
}
