answer.code: In function ‘int main()’:
answer.code:143:29: error: ‘src’ was not declared in this scope
  143 |     cout << mcf.minCostFlow(src, sink).second << '\n';
      |                             ^~~
answer.code:143:34: error: ‘sink’ was not declared in this scope; did you mean ‘sinl’?
  143 |     cout << mcf.minCostFlow(src, sink).second << '\n';
      |                                  ^~~~
      |                                  sinl