#include <bits/stdc++.h>
const int MAXN = 2e5 + 10;
using namespace std;
long long read() {
  long long x = 0, f = 1;
  char ch = getchar();
  while (!isdigit(ch)) {
    if (ch == '-') f = -1;
    ch = getchar();
  }
  while (isdigit(ch)) x = x * 10 + ch - '0', ch = getchar();
  return f * x;
}
int n, q;
long long a[MAXN];
typedef struct node {
  long long maxx;
  long long sum;
} node;
node d[MAXN << 2];
void up(int x) {
  d[x].sum = d[x << 1].sum + d[x << 1 | 1].sum;
  d[x].maxx = max(d[x << 1].maxx, d[x << 1 | 1].maxx);
}
void built(int rt, int l, int r) {
  if (l == r) {
    d[rt].maxx = d[rt].sum = a[l];
    return;
  }
  int mid = (l + r) >> 1;
  built(rt << 1, l, mid);
  built(rt << 1 | 1, mid + 1, r);
  up(rt);
}
void update(int rt, int l, int r, int t, long long vul) {
  if (l == r) {
    d[rt].maxx = d[rt].sum = vul;
    return;
  }
  int mid = (l + r) >> 1;
  if (t <= mid)
    update(rt << 1, l, mid, t, vul);
  else
    update(rt << 1 | 1, mid + 1, r, t, vul);
  up(rt);
}
bool flag;
int pos1;
void querty2(int rt, int l, int r, long long vul) {
  if (l == r) {
    pos1 = l;
    return;
  }
  int mid = (l + r) >> 1;
  if (d[rt << 1].maxx >= vul)
    querty2(rt << 1, l, mid, vul);
  else
    querty2(rt << 1 | 1, mid + 1, r, vul);
}
void querty(int rt, int l, int r, int ql, int qr, long long vul) {
  if (flag) return;
  if (ql <= l && r <= qr) {
    if (d[rt].maxx >= vul) {
      flag = 1;
      querty2(rt, l, r, vul);
    }
    return;
  }
  int mid = (l + r) >> 1;
  if (ql <= mid) querty(rt << 1, l, mid, ql, qr, vul);
  if (qr > mid) querty(rt << 1 | 1, mid + 1, r, ql, qr, vul);
}
long long ans;
void querty1(int rt, int l, int r, int ql, int qr) {
  if (ql <= l && r <= qr) {
    ans += d[rt].sum;
    return;
  }
  int mid = (l + r) >> 1;
  if (ql <= mid) querty1(rt << 1, l, mid, ql, qr);
  if (qr > mid) querty1(rt << 1 | 1, mid + 1, r, ql, qr);
}
int main() {
  n = read();
  q = read();
  for (int i = 1; i <= n; i++) a[i] = read();
  a[n + 1] = 1e18;
  int pos, ans1;
  long long vul, key, pre;
  n++;
  built(1, 1, n);
  for (int i = 1; i <= q; i++) {
    pos = read();
    vul = read();
    a[pos] = vul;
    update(1, 1, n, pos, vul);
    ans1 = -1;
    key = 0;
    if (!a[1]) {
      printf("1\n");
      continue;
    }
    if (a[1] == a[2]) {
      printf("2\n");
      continue;
    }
    key = a[1] + a[2];
    pre = 3;
    while (1) {
      if (pre > n) break;
      flag = 0;
      querty(1, 1, n, pre, n, key);
      ans = 0;
      querty1(1, 1, n, 1, pos1 - 1);
      if (ans == a[pos1]) {
        ans1 = pos1;
        break;
      }
      key = ans + a[pos1];
      pre = pos1 + 1;
    }
    printf("%d\n", ans1);
  }
  return 0;
}
