Language: C++

#include <bits/stdc++.h>
using namespace std;
const double pi=2*acos(0.0);
double inff=1.0/0.0;
#define ll           long long int
#define inf          1000000000000000008
#define MOD          1000000007
#define pb           push_back
#define sz(x)        (int)x.size()
#define mp           make_pair
#define lbd          lower_bound
#define ubd          upper_bound
#define ipair        pair<ll,ll> 
#define all(v)       v.begin(),v.end()
#define watch(x)     cout<<(#x)<<" is "<<(x)<<endl;
#define rep(a,b,c)   for(a=(int)b;a<(int)c;a++)
#define rep2(a,b,c)  for(a=(int)b;a<(int)c;a+=2)  
#define bac(a,b,c)   for(a=(int)b;a>=(int)c;a--)
#define se           second
#define f            first
#define ios          ios::sync_with_stdio(false), cout.tie(0), cin.tie(0);
#define mem(a,val)   memset(a,val,sizeof a)
#define endl         "\n"
#define mxn          200001
#define vi           vector<ll>
#define vii          vector<ipair> 
#define si           set<ll> 
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
/*Variables Start*/
ll x,y,n,i,z,j,k,w,u,q,m,t;
vii hero;vi v;
/*Variables End*/
void solve()
{
 	cin>>x>>y;
 	if((x+y)&1)
 	{
 		cout<<"IMPOSSIBLE"<<endl;
 	} 
 	else cout<<(x+y)/2<<endl;
}
int main() 
{ 
  int TESTS=1;
  ios;  
  cin>>TESTS;
  while(TESTS--)
  {
    solve();
  }  
}#include <bits/stdc++.h>
using namespace std;
const double pi=2*acos(0.0);
double inff=1.0/0.0;
#define ll           long long int
#define inf          1000000000000000008
#define MOD          1000000007
#define pb           push_back
#define sz(x)        (int)x.size()
#define mp           make_pair
#define lbd          lower_bound
#define ubd          upper_bound
#define ipair        pair<ll,ll> 
#define all(v)       v.begin(),v.end()
#define watch(x)     cout<<(#x)<<" is "<<(x)<<endl;
#define rep(a,b,c)   for(a=(int)b;a<(int)c;a++)
#define rep2(a,b,c)  for(a=(int)b;a<(int)c;a+=2)  
#define bac(a,b,c)   for(a=(int)b;a>=(int)c;a--)
#define se           second
#define f            first
#define ios          ios::sync_with_stdio(false), cout.tie(0), cin.tie(0);
#define mem(a,val)   memset(a,val,sizeof a)
#define endl         "\n"
#define mxn          200001
#define vi           vector<ll>
#define vii          vector<ipair> 
#define si           set<ll> 
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
/*Variables Start*/
ll x,y,n,i,z,j,k,w,u,q,m,t;
vii hero;vi v;
/*Variables End*/
void solve()
{
 	cin>>x>>y;
 	if((x+y)&1)
 	{
 		cout<<"IMPOSSIBLE"<<endl;
 	} 
 	else cout<<(x+y)/2<<endl;
}
int main() 
{ 
  int TESTS=1;
  ios;  
  while(TESTS--)
  {
    solve();
  }  
}

Compiler output:
a.cc:51:2: error: stray '#' in program
   51 | }#include <bits/stdc++.h>
      |  ^
a.cc:51:3: error: 'include' does not name a type
   51 | }#include <bits/stdc++.h>
      |   ^~~~~~~
a.cc:53:14: error: redefinition of 'const double pi'
   53 | const double pi=2*acos(0.0);
      |              ^~
a.cc:3:14: note: 'const double pi' previously defined here
    3 | const double pi=2*acos(0.0);
      |              ^~
a.cc:54:8: error: redefinition of 'double inff'
   54 | double inff=1.0/0.0;
      |        ^~~~
a.cc:4:8: note: 'double inff' previously declared here
    4 | double inff=1.0/0.0;
      |        ^~~~
a.cc:78:12: error: redefinition of 'std::mt19937_64 rng'
   78 | mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
      |            ^~~
a.cc:28:12: note: 'std::mt19937_64 rng' previously declared here
   28 | mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
      |            ^~~
a.cc:80:4: error: redefinition of 'long long int x'
   80 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |    ^
a.cc:30:4: note: 'long long int x' previously declared here
   30 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |    ^
a.cc:80:6: error: redefinition of 'long long int y'
   80 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |      ^
a.cc:30:6: note: 'long long int y' previously declared here
   30 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |      ^
a.cc:80:8: error: redefinition of 'long long int n'
   80 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |        ^
a.cc:30:8: note: 'long long int n' previously declared here
   30 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |        ^
a.cc:80:10: error: redefinition of 'long long int i'
   80 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |          ^
a.cc:30:10: note: 'long long int i' previously declared here
   30 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |          ^
a.cc:80:12: error: redefinition of 'long long int z'
   80 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |            ^
a.cc:30:12: note: 'long long int z' previously declared here
   30 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |            ^
a.cc:80:14: error: redefinition of 'long long int j'
   80 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |              ^
a.cc:30:14: note: 'long long int j' previously declared here
   30 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |              ^
a.cc:80:16: error: redefinition of 'long long int k'
   80 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |                ^
a.cc:30:16: note: 'long long int k' previously declared here
   30 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |                ^
a.cc:80:18: error: redefinition of 'long long int w'
   80 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |                  ^
a.cc:30:18: note: 'long long int w' previously declared here
   30 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |                  ^
a.cc:80:20: error: redefinition of 'long long int u'
   80 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |                    ^
a.cc:30:20: note: 'long long int u' previously declared here
   30 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |                    ^
a.cc:80:22: error: redefinition of 'long long int q'
   80 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |                      ^
a.cc:30:22: note: 'long long int q' previously declared here
   30 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |                      ^
a.cc:80:24: error: redefinition of 'long long int m'
   80 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |                        ^
a.cc:30:24: note: 'long long int m' previously declared here
   30 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |                        ^
a.cc:80:26: error: redefinition of 'long long int t'
   80 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |                          ^
a.cc:30:26: note: 'long long int t' previously declared here
   30 | ll x,y,n,i,z,j,k,w,u,q,m,t;
      |                          ^
a.cc:81:5: error: redefinition of 'std::vector<std::pair<long long int, long long int> > hero'
   81 | vii hero;vi v;
      |     ^~~~
a.cc:31:5: note: 'std::vector<std::pair<long long int, long long int> > hero' previously declared here
   31 | vii hero;vi v;
      |     ^~~~
a.cc:81:13: error: redefinition of 'std::vector<long long int> v'
   81 | vii hero;vi v;
      |             ^
a.cc:31:13: note: 'std::vector<long long int> v' previously declared here
   31 | vii hero;vi v;
      |             ^
a.cc:83:6: error: redefinition of 'void solve()'
   83 | void solve()
      |      ^~~~~
a.cc:33:6: note: 'void solve()' previously defined here
   33 | void solve()
      |      ^~~~~
a.cc:92:5: error: redefinition of 'int main()'
   92 | int main()
      |     ^~~~
a.cc:42:5: note: 'int main()' previously defined here
   42 | int main()
      |     ^~~~