Language: C++

#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;

int main() {
	int N, M;
	long long int ans = 0;
	cin >> N>> M;
	//vector< long int >L;
	vector<pair<int, int >>pairs(N);
	vector<int> A(N), B(N);
	for (long  int i = 0; i < N; i++) {
		//long  int A,B;
		cin >> A[i];
		cin >> B[i];
		pairs[i] = make_pair(A, B);
		/*for ( long int k = 0; k < B; k++) {
			L.push_back(A);
		}*/
	}
	///sort(L.begin(), L.end());
	sort(pairs.begin(), pairs.end());

	for ( int i = 0; i < N; i++) {
		//cout << L[j] << endl;
		//ans += L[j];
		int buy = min(M, pairs[i].second);

		ans += (long long)buy * pairs[i].first;
		M -= buy;

	}
	cout << ans << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:17:42: error: no match for 'operator=' (operand types are '__gnu_cxx::__alloc_traits<std::allocator<std::pair<int, int> >, std::pair<int, int> >::value_type' {aka 'std::pair<int, int>'} and 'std::pair<std::vector<int>, std::vector<int> >')
   17 |                 pairs[i] = make_pair(A, B);
      |                                          ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/string:51,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_pair.h:946:9: note: candidate: 'template<class _U1, class _U2> typename std::enable_if<std::__and_<std::is_assignable<_T1&, const _U1&>, std::is_assignable<_T2&, const _U2&> >::value, std::pair<_T1, _T2>&>::type std::pair<_T1, _T2>::operator=(const std::pair<_U1, _U2>&) [with _U2 = _U1; _T1 = int; _T2 = int]'
  946 |         operator=(const pair<_U1, _U2>& __p)
      |         ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:946:9: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_pair.h: In substitution of 'template<class _U1, class _U2> typename std::enable_if<std::__and_<std::is_assignable<int&, const _U1&>, std::is_assignable<int&, const _U2&> >::value, std::pair<int, int>&>::type std::pair<int, int>::operator=(const std::pair<_T1, _T2>&) [with _U1 = std::vector<int>; _U2 = std::vector<int>]':
a.cc:17:28:   required from here
   17 |                 pairs[i] = make_pair(A, B);
      |                                          ^
/usr/include/c++/14/bits/stl_pair.h:946:9: error: no type named 'type' in 'struct std::enable_if<false, std::pair<int, int>&>'
  946 |         operator=(const pair<_U1, _U2>& __p)
      |         ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:957:9: note: candidate: 'template<class _U1, class _U2> typename std::enable_if<std::__and_<std::is_assignable<_T1&, _U1&&>, std::is_assignable<_T2&, _U2&&> >::value, std::pair<_T1, _T2>&>::type std::pair<_T1, _T2>::operator=(std::pair<_U1, _U2>&&) [with _U2 = _U1; _T1 = int; _T2 = int]'
  957 |         operator=(pair<_U1, _U2>&& __p)
      |         ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:957:9: note:   template argument deduction/substitution failed:
/usr/include/c++/14/bits/stl_pair.h: In substitution of 'template<class _U1, class _U2> typename std::enable_if<std::__and_<std::is_assignable<int&, _U1&&>, std::is_assignable<int&, _U2&&> >::value, std::pair<int, int>&>::type std::pair<int, int>::operator=(std::pair<_T1, _T2>&&) [with _U1 = std::vector<int>; _U2 = std::vector<int>]':
a.cc:17:28:   required from here
   17 |                 pairs[i] = make_pair(A, B);
      |                                          ^
/usr/include/c++/14/bits/stl_pair.h:957:9: error: no type named 'type' in 'struct std::enable_if<false, std::pair<int, int>&>'
  957 |         operator=(pair<_U1, _U2>&& __p)
      |         ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:921:7: note: candidate: 'std::pair<_T1, _T2>& std::pair<_T1, _T2>::operator=(std::__conditional_t<((bool)std::__and_<std::is_copy_assignable<_T1>, std::is_copy_assignable<_T2> >::value), const std::pair<_T1, _T2>&, const std::__nonesuch&>) [with _T1 = int; _T2 = int; std::__conditional_t<((bool)std::__and_<std::is_copy_assignable<_T1>, std::is_copy_assignable<_T2> >::value), const std::pair<_T1, _T2>&, const std::__nonesuch&> = const std::pair<int, int>&]'
  921 |       operator=(__conditional_t<__and_<is_copy_assignable<_T1>,
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:923:65: note:   no known conversion for argument 1 from 'std::pair<std::vector<int>, std::vector<int> >' to 'std::__conditional_t<true, const std::pair<int, int>&, const std::__nonesuch&>' {aka 'const std::pair<int, int>&'}
  921 |       operator=(__conditional_t<__and_<is_copy_assignable<_T1>,
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
  922 |                                        is_copy_assignable<_T2>>::value,
      |                                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  923 |                                 const pair&, const __nonesuch&> __p)
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_pair.h:931:7: note: candidate: 'std::pair<_T1, _T2>& std::pair<_T1, _T2>::operator=(std::__conditional_t<((bool)std::__and_<std::is_move_assignable<_Tp>, std::is_move_assignable<_T2> >::value), std::pair<_T1, _T2>&&, std::__nonesuch&&>) [with _T1 = int; _T2 = int; std::__conditional_t<((bool)std::__and_<std::is_move_assignable<_Tp>, std::is_move_assignable<_T2> >::value), std::pair<_T1, _T2>&&, std::__nonesuch&&> = std::pair<int, int>&&]'
  931 |       operator=(__conditional_t<__and_<is_move_assignable<_T1>,
      |       ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:933:55: note:   no known conversion for argument 1 from 'std::pair<std::vector<int>, std::vector<int> >' to 'std::__conditional_t<true, std::pair<int, int>&&, std::__nonesuch&&>' {aka 'std::pair<int, int>&&'}
  931 |       operator=(__conditional_t<__and_<is_move_assignable<_T1>,
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  932 |                                        is_move_assignable<_T2>>::value,
      |                                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  933 |                                 pair&&, __nonesuch&&> __p)
      |                                 ~~~~~~~~~~~~~~~~~~~~~~^~~