Help me in solving Sum of Four Values

help
1

Problem
Here’s my code :

#include <bits/stdc++.h>
#define int long long
#define vi vector<int>
#define ii pair<int,int>
#define iii unordered_map<int,ii>
using namespace std;

void setIO() {
  cin.tie(0)->ios_base::sync_with_stdio(0);
}

void solve() {
  int n,x;
  cin >> n >> x;
  vi a(n);
  iii si;
  for(auto &e : a) cin >> e;
  for(int i = 0;i < n;++i) {
    for(int j = i+1;j < n;++j) {
      int x2 = x-a[i]-a[j];
      if(si.find(x2) != si.end()) {
        cout << i+1 << ' ' << j+1 << ' ' << si[x2].first+1 << ' ' << si[x2].second+1;
        return;
      }
      si[a[i]+a[j]] = {i,j};
    }
  }
  cout << "IMPOSSIBLE";
}

int32_t main() {
  setIO();
  solve();
  return 0;
}

There’s something wrong going the logic here. Help me identify n fix it