Language: C++

#include<bits/stdc++.h>
#define vll vector<ll>
#define vi vector<int>
#define vpll vector<pair<ll,ll>>
#define pii pair<int,int>
#define REP(i,a) for(int (i)=0; (i)<(a); (i)++)
#define RREP(i,a) for(int (i)=a-1; (i)>=(0); (i)--)
#define REP2(i,a,b) for(int (i)=(a); (i)<(b); (i)++)
#define MOD 1000000007
#define ALL(v) v.begin(), v.end()
#define m0(x) memset(x,0,sizeof(x))
typedef long long ll;

using namespace std;

int gcd(int a,int b){return b?gcd(b,a%b):a;}
int dx[4]={1,0,-1,0};
int dy[4]={0,1,0,-1};



int main(){
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ll N;
  cin>>N;
  cin >> N*(N-1)/2;
  return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:27:7: error: no match for 'operator>>' (operand types are 'std::istream' {aka 'std::basic_istream<char>'} and 'll' {aka 'long long int'})
   27 |   cin >> N*(N-1)/2;
      |   ~~~ ^~ ~~~~~~~~~
      |   |             |
      |   |             ll {aka long long int}
      |   std::istream {aka std::basic_istream<char>}
In file included from /usr/include/c++/14/sstream:40,
                 from /usr/include/c++/14/complex:45,
                 from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127,
                 from a.cc:1:
/usr/include/c++/14/istream:170:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(bool&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  170 |       operator>>(bool& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:170:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:17: error: cannot bind non-const lvalue reference of type 'bool&' to a value of type 'll' {aka 'long long int'}
   27 |   cin >> N*(N-1)/2;
      |          ~~~~~~~^~
/usr/include/c++/14/istream:174:7: note: candidate: 'std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(short int&) [with _CharT = char; _Traits = std::char_traits<char>]' (near match)
  174 |       operator>>(short& __n);
      |       ^~~~~~~~
/usr/include/c++/14/istream:174:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:17: error: cannot bind non-const lvalue reference of type 'short int&' to a value of type 'll' {aka 'long long int'}
   27 |   cin >> N*(N-1)/2;
      |          ~~~~~~~^~
/usr/include/c++/14/istream:177:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(short unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  177 |       operator>>(unsigned short& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:177:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:17: error: cannot bind non-const lvalue reference of type 'short unsigned int&' to a value of type 'll' {aka 'long long int'}
   27 |   cin >> N*(N-1)/2;
      |          ~~~~~~~^~
/usr/include/c++/14/istream:181:7: note: candidate: 'std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(int&) [with _CharT = char; _Traits = std::char_traits<char>]' (near match)
  181 |       operator>>(int& __n);
      |       ^~~~~~~~
/usr/include/c++/14/istream:181:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:17: error: cannot bind non-const lvalue reference of type 'int&' to a value of type 'll' {aka 'long long int'}
   27 |   cin >> N*(N-1)/2;
      |          ~~~~~~~^~
/usr/include/c++/14/istream:184:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  184 |       operator>>(unsigned int& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:184:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:17: error: cannot bind non-const lvalue reference of type 'unsigned int&' to a value of type 'll' {aka 'long long int'}
   27 |   cin >> N*(N-1)/2;
      |          ~~~~~~~^~
/usr/include/c++/14/istream:188:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  188 |       operator>>(long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:188:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:17: error: cannot bind non-const lvalue reference of type 'long int&' to a value of type 'll' {aka 'long long int'}
   27 |   cin >> N*(N-1)/2;
      |          ~~~~~~~^~
/usr/include/c++/14/istream:192:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  192 |       operator>>(unsigned long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:192:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:17: error: cannot bind non-const lvalue reference of type 'long unsigned int&' to a value of type 'll' {aka 'long long int'}
   27 |   cin >> N*(N-1)/2;
      |          ~~~~~~~^~
/usr/include/c++/14/istream:199:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  199 |       operator>>(long long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:199:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:17: error: cannot bind non-const lvalue reference of type 'long long int&' to an rvalue of type 'll' {aka 'long long int'}
   27 |   cin >> N*(N-1)/2;
      |          ~~~~~~~^~
/usr/include/c++/14/istream:203:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  203 |       operator>>(unsigned long long& __n)
      |       ^~~~~~~~
/usr/include/c++/14/istream:203:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:17: error: cannot bind non-const lvalue reference of type 'long long unsigned int&' to a value of type 'll' {aka 'long long int'}
   27 |   cin >> N*(N-1)/2;
      |          ~~~~~~~^~
/usr/include/c++/14/istream:219:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(float&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  219 |       operator>>(float& __f)
      |       ^~~~~~~~
/usr/include/c++/14/istream:219:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:17: error: cannot bind non-const lvalue reference of type 'float&' to a value of type 'll' {aka 'long long int'}
   27 |   cin >> N*(N-1)/2;
      |          ~~~~~~~^~
/usr/include/c++/14/istream:223:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(double&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  223 |       operator>>(double& __f)
      |       ^~~~~~~~
/usr/include/c++/14/istream:223:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:17: error: cannot bind non-const lvalue reference of type 'double&' to a value of type 'll' {aka 'long long int'}
   27 |   cin >> N*(N-1)/2;
      |          ~~~~~~~^~
/usr/include/c++/14/istream:227:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long double&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  227 |       operator>>(long double& __f)
      |       ^~~~~~~~
/usr/include/c++/14/istream:227:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:17: error: cannot bind non-const lvalue reference of type 'long double&' to a value of type 'll' {aka 'long long int'}
   27 |   cin >> N*(N-1)/2;
      |          ~~~~~~~^~
/usr/include/c++/14/istream:328:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(void*&) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  328 |       operator>>(void*& __p)
      |       ^~~~~~~~
/usr/include/c++/14/istream:328:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:17: error: invalid conversion from 'll' {aka 'long long int'} to 'void*' [-fpermissive]
   27 |   cin >> N*(N-1)/2;
      |          ~~~~~~~^~
      |                 |
      |                 ll {aka long long int}
a.cc:27:17: error: cannot bind rvalue '(void*)((N * (N - 1)) / 2)' to 'void*&'
/usr/include/c++/14/istream:122:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(__istream_type& (*)(__istream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  122 |       operator>>(__istream_type& (*__pf)(__istream_type&))
      |       ^~~~~~~~
/usr/include/c++/14/istream:122:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:17: error: invalid conversion from 'll' {aka 'long long int'} to 'std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&)' {aka 'std::basic_istream<char>& (*)(std::basic_istream<char>&)'} [-fpermissive]
   27 |   cin >> N*(N-1)/2;
      |          ~~~~~~~^~
      |                 |
      |                 ll {aka long long int}
/usr/include/c++/14/istream:126:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(__ios_type& (*)(__ios_type&)) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>; __ios_type = std::basic_ios<char>]' (near match)
  126 |       operator>>(__ios_type& (*__pf)(__ios_type&))
      |       ^~~~~~~~
/usr/include/c++/14/istream:126:7: note:   conversion of argument 1 would be ill-formed:
a.cc:27:17: error: invalid conversion from 'll' {aka 'long long int'} to 'std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&)' {aka 'std::basic_ios<char>& (*)(std::basic_ios<char>&)'} [-fpermissive]
   27 |   cin >> N*(N-1)/2;
      |          ~~~