Language: C++

/***************************************************************************\
                                                                            !
                           JUBAYER ABDULLAH JOY                             !
                  5th Batch, CSE, University of Barishal                    !
            Codeforces = Joy     !!     CodeChef = jubayer_joy              !
            Mail = joy.cse5.bu@gmail.com !! jubayerjoy98@gmail.com          !
                                                                            !
/***************************************************************************/

#pragma GCC optimize("Ofast,inline,unroll-loops,fast-math")
#include<bits/stdc++.h>
using namespace std;

typedef     long long               ll;
typedef     unsigned long long      ull;
typedef     long double             ld;
typedef     vector<int>             vi;
typedef     vector<ll>              vl;
typedef     pair<ll,ll>             pl;
typedef     pair<int, int>          pi;

#define     ff          first
#define     ss          second
#define     pb          push_back
#define     pf          push_front
#define     mp          make_pair
#define     gcd(a,b)    __gcd(a,b)
#define     lcm(a,b)    (a) * ((b) / gcd(a,b))
#define     f(i,n)      for(ull i=0; i<(n); i++)
#define     all(v)      v.begin(), v.end()
#define     Sort(v)     sort(all(v))
#define     rev(v)      reverse(all(v))
#define     bitcount    __builtin_popcountll
#define     YES         printf("YES\n")
#define     NO          printf("NO\n")
#define     spc         " "
#define     el          "\n"
#define     die         return 0
#ifdef      Joy
#define     io
#define     D(args...)  do { cerr<<"DEBUG > Line : "<<__LINE__ <<el<<#args<<" : ";dbg(args);} while(0)
#elif
#define     io          ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
#define     D(args...)
#endif
/***        Use Carefully, Needs more Work ***/
#define     _T          template<typename T, typename... Types>
#define     _Tos        template <typename T> ostream &operator
#define     _Tfs        template < typename F, typename S > ostream &operator
auto mini(auto x) {return x;}   _T auto mini(T a, Types... b) {auto x = (a) < mini(b...)?a:mini(b...); return x; }
auto maxi(auto x) {return x;}   _T auto maxi(T a, Types... b) {auto x = (a) > maxi(b...)?a:maxi(b...); return x; }
auto sum() {return 0;}          _T auto sum (T a, Types... b) {return (a) + sum(b...); }
auto product() {return 1;}      _T auto product(T a, Types... b) {return (a) * product(b...); }
void in() {return;}             _T void in(T &a, Types&... b)    {cin>>(a); in(b...);}
void out() {return;}            _T void out(T a, Types... b)     {cout<<(a); out(b...);}
void outln(){cout<<el; return;} _T void outln(T a, Types... b)   {cout<<(a); outln(b...);}
void dbg () { cerr << el; }     _T void dbg( T a, Types... b)    {cerr<<(a)<<' '; dbg(b...); }

_Tos << (ostream &os, vector        <T> &v)     { for(auto i : v) os<<(i)<<spc; return os << el; }
_Tos << (ostream &os, set           <T> &v)     { for(auto i : v) os<<(i)<<spc; return os << el; }
_Tos << (ostream &os, multiset      <T> &v)     { for(auto i : v) os<<(i)<<spc; return os << "\n"; }
_Tos << (ostream &os, unordered_set <T> &v)     { for(auto i : v) os<<(i)<<spc; return os << "\n"; }
_Tos << (ostream &os, stack         <T> &v)     { while(!v.empty()) {os<<(v.top())<<spc; v.pop();}return os<<el;}
_Tos << (ostream &os, priority_queue<T> &v)     { while(!v.empty()) {os<<(v.top())<<spc; v.pop();}return os<<el;}
_Tos << (ostream &os, queue         <T> &v)     { while(!v.empty()) {os<<(v.front())<<spc; v.pop();}return os<<el;}
_Tfs << (ostream &os, pair          <F,S> &p)   { return os<<"\n("<<(p.first)<<", "<<(p.second) << ")";}
_Tfs << (ostream &os, map           <F,S> &v)   { for(auto i : v) os<<el<<(i.first)<<" = "<<(i.second);return os<<el;}
_Tfs << (ostream &os, multimap      <F,S> &v)   { for(auto i : v) os<<el<<(i.first)<<" = "<<(i.second);return os<<el;}
_Tfs << (ostream &os, unordered_map <F,S> &v)   { for(auto i : v) os<<el<<(i.first)<<" = "<<(i.second);return os<<el;}

/*** Movement ***/
#define valid(new_x,new_y,row,column)  (new_x)>=0 && (new_x)<(row) && (new_y)>=0 && (new_y)<(column)
//vi fx={+1,-1,+0,+0};             // Four Direction
//vi fy={+0,+0,+1,-1};             // Four Direction
//vi fx={+0,+0,+1,-1,-1,+1,-1,+1}; // Kings Move - 8 Direction
//vi fy={-1,+1,+0,+0,+1,+1,-1,-1}; // Kings Move - 8 Direction
//vi fx={-2,-2,-1,-1,+1,+1,+2,+2}; // Knights Move
//vi fy={-1,+1,-2,+2,-2,+2,-1,+1}; // Knights Move

//vector<vi> matrix(row, vi (column,value)); //- 2D Vector
//cout << fixed << setprecision(20)<< value <<endl;
//sort(all(a), greater <int>());


int main(int argc, char const *argv[])
{
    io

    int n, m;
    in(n,m);
    out(n*(n-1)/2 + m*(m-1)/2);










    return 0;
}













Compiler output:
a.cc:42:6: error: #elif with no expression
   42 | #elif
      |      ^
a.cc:50:11: warning: use of 'auto' in parameter declaration only available with '-std=c++20' or '-fconcepts'
   50 | auto mini(auto x) {return x;}   _T auto mini(T a, Types... b) {auto x = (a) < mini(b...)?a:mini(b...); return x; }
      |           ^~~~
a.cc:51:11: warning: use of 'auto' in parameter declaration only available with '-std=c++20' or '-fconcepts'
   51 | auto maxi(auto x) {return x;}   _T auto maxi(T a, Types... b) {auto x = (a) > maxi(b...)?a:maxi(b...); return x; }
      |           ^~~~
a.cc: In function 'int main(int, const char**)':
a.cc:87:5: error: 'io' was not declared in this scope; did you mean 'in'?
   87 |     io
      |     ^~
      |     in
a.cc:90:8: error: 'n' was not declared in this scope; did you mean 'yn'?
   90 |     in(n,m);
      |        ^
      |        yn
a.cc:90:10: error: 'm' was not declared in this scope; did you mean 'tm'?
   90 |     in(n,m);
      |          ^
      |          tm