CSES - Shared codeLink to this code: `https://cses.fi/paste/93e2e3b621eed69579e8b4/`
```#include <bits/stdc++.h>
using namespace std;

#ifndef ONLINE_JUDGE
#include "/Users/gaurav/Desktop/cppvscode/debug.h"
#else
#define dbg(...);
#define debug(...);
//#define crndl;
#endif

#define ll long long

#define int ll

#define          all(v)              v.begin(), v.end()
#define ll long long
const ll MOD = 1e9+1;
const ll MAX = 1e5 + 13;
#define int ll
#define printArr(arr) for(auto &i: arr){cout<<i<<" ";}cout<<endl;
#define inp(n, v) for(int i = 0; i < n; i++){ int a; cin >> a; v.push_back(a); }

vector<bool> Primes(MOD, 1);
int fact[MAX + 1];

int GCD(int a, int b) {
while(b) {
int t = a;
a = b;
b = t % b;
}
return a;
}

void sieve_func(int n) {
Primes[0] = Primes[1] = false;
for (int i = 2; i <= n; i++) {
if (Primes[i] && (long long)i * i <= n) {
for (int j = i * i; j <= n; j += i)
Primes[j] = false;
}
}
}

int power(int a, int b) {
int res = 1;
while(b) {
if(b & 1)
res *= a;
a *= a;
b >>= 1;
}
return res;
}

int powerMOD(int a, int b) {
a %= MOD;
int res = 1;
while(b) {
if(b & 1)
res = (res * a) % MOD;
a = (a * a) % MOD;
b >>= 1;
}
return res;
}

int inverse(int n) {
return power(n, MOD - 2); // Fermet's Little Theorem
}

void fac() {
fact[0] = 1;
for(int i = 1; i <= MAX; i++)
fact[i] = fact[i - 1] * i % MOD;
}

int ncr(int n, int r) {
return fact[n] * inverse(fact[r] * fact[n - r]) % MOD;
}

int npr(int n, int r) {
return fact[n] * inverse(fact[n - r]);
}

int lcm(int x,int y){
int res = x * y / (GCD(x,y));
return res;
}

int log2Bit(int n) {
int i = 0;
int ans = -1;
while(n > 0) {
if(n & 1)
ans = i;
n = n >> 1;
i++;
}
return ans;
}

double sqrtb(double n) {
double i = 1;
double j = n;
while(j - i > 1e-10) {
double mid = i + (j - i) / 2;
if(mid * mid <= n)
i = mid;
else
j = mid;
}
return i;
}

//--------------------Code Here-------------------------------//

void solve() {

unordered_map<int,int>mp;
for(int i = 0; i< n; i++){
int a; cin>>a;
if(mp.find(a) != mp.end()){
int b = mp[a]+1;
cout<<b<<" "<<i+1<<endl;
return;
}
else{
mp[x-a] = i;
}
}
cout<<"IMPOSSIBLE"<<endl;

}

//______________________ End .__________________________________//
// Important things.  //
// check you took the right test case
// dont stay on one method or approach for long
// check the value of T below sometimes they don't give it;
// always check if the vector size is defined v(n);

signed main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);

#ifndef ONLINE_JUDGE
freopen("/Users/gaurav/Desktop/cppvscode/error.txt", "w", stderr);
#endif

int T = 1;
//cin >> T;
for(int i = 0; i < T; i++) {
debug(testCase, i + 1);
solve();
}
return 0;
}

```