Language: C++

/*Ph@n^0m Dec0d3r*/
/*----------------*/
/* 	^_HAR HAR MAHADEV_^
   	|Om namah shivaya|
*/
#include<bits/stdc++.h>
//#include<boost/multiprecision/cpp_int.hpp>
#define f(i,a,b) for(int i=a;i<b;i++)
#define ll long long int
#define fast std::ios_base::sync_with_stdio(false),cin.tie(0),cout.tie(0)
#define pb(temp) push_back(temp)
#define mp make_pair
#define mod (ll)1000000007
//using namespace boost::multiprecision;
using namespace std ;
typedef unsigned long long int ulli;

ulli gcd(ulli x,ulli y)
{
    if(x==0) return y;
    return gcd(y%x,x);
}
ulli factorial(ulli n)
{
    if (n == 0)
    return 1;
    return n * factorial(n - 1);
}
ll findS(ll s)
{
	return (sqrtl(8*s + 1) - 1)/2;
}
ll prime(ll a){
    if(a==1)return 0;
    if(a==2 || a==3)return true;
    if(a%2==0 ||a%3==0)return 0;
    for(ll i=5;i<=sqrt(a);i+=6)
        if(a%i==0 || a%(i+2)==0)
            return 0;

    return 1;
}
ll power(ll x,ll y)
{
    if (y == 0)
        return 1;
    ll p = power(x, y/2) % mod;
    p = (p * p) % mod;

    return (y%2 == 0)? p : (x * p) % mod;
}
ll powermod(ll x,ll y)
{
    ll res = 1;
    x = x % mod;
    while (y > 0)
    {
        if (y & 1)
            res = (res*x) % mod;
        y = y>>1;
        x = (x*x) % mod;
    }
    return res;
}
ll nCr(ll n,ll k)
{
    ll C[k+1];
    //memset(C, 0, sizeof(C));

    C[0] = 1;

    for (ll i = 1; i <= n; i++)
    {
        for (ll j = min(i, k); j > 0; j--)
            C[j] = (C[j] + C[j-1])%(ll)(1e9 + 7);
    }
    return C[k];
}
ll LOGN(ll n , ll r){
	return (n > r-1) ? (1 + LOGN(n / r , r)) : 0 ;
}
void dfs(vector<ll> v[], bool visited[], ll current_node){
	visited[current_node]=true;
	for(ll nxt_node : v[current_node]){
		if(visited[nxt_node]==false){
			dfs(v , visited, nxt_node);
		}
	}
	return;
}

void bfs(vector<ll> v[], bool visited[], ll root){

    int current_node;
    queue<int> q;

    q.push(root);

    while(!q.empty()){

        current_node=q.front();

        visited[current_node]=true;

        for(int x:v[current_node])
            if(!visited[x])
                q.push(x);
    }
}
ll computeXOR(ll n)
{
    switch(n & 3)
    {
    case 0: return n;     
    case 1: return 1;     
    case 2: return n + 1;
    case 3: return 0;    
    }
}
void scanll(ll &x)
{
	register long long c;
	bool flag = false;
	x = 0;
	for(;((c<48 && c!=45) || c>57);c = gc());
	if(c==45)
	{
		flag = true;
		c = gc();
	}
	for(;c>47 && c<58;c = gc()) {x = (x<<1) + (x<<3) + c - 48;}
	if(flag)
    	x = x - (x<<1);
	return;
}
int maxSubArraySum(int a[], int size)
{
   int max_so_far = a[0];
   int curr_max = a[0];
   for (int i = 1; i < size; i++)
   {
        curr_max = max(a[i], curr_max+a[i]);
        max_so_far = max(max_so_far, curr_max);
   }
   return max_so_far;
}
int main(){
	fast;
	string s , t ;
  cin >> s >> t ;
  cout << (t+s)  ;
}


Compiler output:
a.cc: In function 'void scanll(long long int&)':
a.cc:122:28: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
  122 |         register long long c;
      |                            ^
a.cc:125:44: error: 'gc' was not declared in this scope; did you mean 'c'?
  125 |         for(;((c<48 && c!=45) || c>57);c = gc());
      |                                            ^~
      |                                            c
a.cc:129:21: error: 'gc' was not declared in this scope; did you mean 'c'?
  129 |                 c = gc();
      |                     ^~
      |                     c
a.cc:131:31: error: 'gc' was not declared in this scope; did you mean 'c'?
  131 |         for(;c>47 && c<58;c = gc()) {x = (x<<1) + (x<<3) + c - 48;}
      |                               ^~
      |                               c
a.cc: In function 'long long int computeXOR(long long int)':
a.cc:119:1: warning: control reaches end of non-void function [-Wreturn-type]
  119 | }
      | ^