Language: C++

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

#define REP(i, n) for(int (i) = 0; (i) < (n); ++(i))
#define REPR(i, n) for(int (i) = (n); (i) >= 0; --(i))
#define FOR(i, n, m) for(ll (i) = (n); (i) < (m); ++(i))

constexpr int INF = 1e9;
//constexpr ll INF = 1LL<<61;

constexpr ll mod = 1e9+7;

double A, B, N;
ll cal(ll x){
  return ll(floor(A*x/B) - A*floor(x/B));
}

int main(){
  cin >> A >> B >> N;
  ll ans = max(cal(min(B-1, N)), cal(N));
  ans = max(ans, cal(min(B, N)));
  FOR(i, (ll)B, (ll)min(B+A+1, N+1)){
    ans = max(ans, cal(i));
  }
  FOR(i, ll(max(0LL, (ll)N-A)), (ll)N){
    ans = max(ans, cal(i));
  }
  cout << ans << endl;
  return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:26:16: error: no matching function for call to 'max(long long int, double)'
   26 |   FOR(i, ll(max(0LL, (ll)N-A)), (ll)N){
      |             ~~~^~~~~~~~~~~~~~
a.cc:7:36: note: in definition of macro 'FOR'
    7 | #define FOR(i, n, m) for(ll (i) = (n); (i) < (m); ++(i))
      |                                    ^
In file included from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_algobase.h:257:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::max(const _Tp&, const _Tp&)'
  257 |     max(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:257:5: note:   template argument deduction/substitution failed:
a.cc:26:16: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'double')
   26 |   FOR(i, ll(max(0LL, (ll)N-A)), (ll)N){
      |             ~~~^~~~~~~~~~~~~~
a.cc:7:36: note: in definition of macro 'FOR'
    7 | #define FOR(i, n, m) for(ll (i) = (n); (i) < (m); ++(i))
      |                                    ^
/usr/include/c++/14/bits/stl_algobase.h:303:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::max(const _Tp&, const _Tp&, _Compare)'
  303 |     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:303:5: note:   candidate expects 3 arguments, 2 provided
In file included from /usr/include/c++/14/algorithm:61:
/usr/include/c++/14/bits/stl_algo.h:5706:5: note: candidate: 'template<class _Tp> constexpr _Tp std::max(initializer_list<_Tp>)'
 5706 |     max(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5706:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5716:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::max(initializer_list<_Tp>, _Compare)'
 5716 |     max(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5716:5: note:   template argument deduction/substitution failed:
a.cc:26:16: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   26 |   FOR(i, ll(max(0LL, (ll)N-A)), (ll)N){
      |             ~~~^~~~~~~~~~~~~~
a.cc:7:36: note: in definition of macro 'FOR'
    7 | #define FOR(i, n, m) for(ll (i) = (n); (i) < (m); ++(i))
      |                                    ^