#include <bits/stdc++.h>
using namespace std;
const int MOD = (int)1e9 + 7;
const int MOD2 = MOD + 2;
const int INF = (int)1e9;
const long long LINF = (long long)1e18;
const long double PI = acos((long double)-1);
const long double EPS = 1e-9;
inline long long gcd(long long a, long long b) {
  long long r;
  while (b) {
    r = a % b;
    a = b;
    b = r;
  }
  return a;
}
inline long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }
inline long long fpow(long long n, long long k, int p = MOD) {
  long long r = 1;
  for (; k; k >>= 1) {
    if (k & 1) r = r * n % p;
    n = n * n % p;
  }
  return r;
}
template <class T>
inline int chkmin(T& a, const T& val) {
  return val < a ? a = val, 1 : 0;
}
template <class T>
inline int chkmax(T& a, const T& val) {
  return a < val ? a = val, 1 : 0;
}
inline long long isqrt(long long k) {
  long long r = sqrt(k) + 1;
  while (r * r > k) r--;
  return r;
}
inline long long icbrt(long long k) {
  long long r = cbrt(k) + 1;
  while (r * r * r > k) r--;
  return r;
}
inline void addmod(int& a, int val, int p = MOD) {
  if ((a = (a + val)) >= p) a -= p;
}
inline void submod(int& a, int val, int p = MOD) {
  if ((a = (a - val)) < 0) a += p;
}
inline int mult(int a, int b, int p = MOD) { return (long long)a * b % p; }
inline int inv(int a, int p = MOD) { return fpow(a, p - 2, p); }
inline int sign(long double x) { return x < -EPS ? -1 : x > +EPS; }
inline int sign(long double x, long double y) { return sign(x - y); }
int modulo(int a, int b) { return (a % b + b) % b; }
vector<long long> BIT(220001, 0), a(220001);
int n;
void update(int idx, long long val) {
  for (int i = idx; i <= n; i += i & -i) {
    BIT[i] += val;
  }
}
long long sum(int idx) {
  long long sum = 0;
  for (int i = idx; i > 0; i -= i & -i) {
    sum += BIT[i];
  }
  return sum;
}
int find_first(long long s) {
  int low = 0, high = n + 1;
  while (low < high) {
    int mid = (low + high) / 2;
    if (sum(mid) >= s)
      high = mid;
    else
      low = mid + 1;
  }
  return low;
}
int query() {
  if (BIT[1] == 0) return 1;
  long long s = BIT[1];
  while (true) {
    int index = find_first(2 * s);
    if (index > n) return -1;
    s = sum(index);
    if (2 * a[index] == s) return index;
  }
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  int q;
  cin >> n >> q;
  for (int i = (1); i <= (n); i++) {
    cin >> a[i];
    update(i, a[i]);
  }
  for (int i = (1); i <= (q); i++) {
    int p;
    long long x;
    cin >> p >> x;
    update(p, x - a[p]);
    a[p] = x;
    cout << query() << endl;
  }
  return 0;
}
