foo.cc: In function 'long long int dfs(long long int)':
foo.cc:26:9: warning: empty parentheses were disambiguated as a function declaration [-Wvexing-parse]
   26 | int main()
      |         ^~
foo.cc:26:9: note: remove parentheses to default-initialize a variable
   26 | int main()
      |         ^~
      |         --
foo.cc:26:9: note: or replace parentheses with braces to value-initialize a variable
foo.cc:27:1: error: a function-definition is not allowed here before '{' token
   27 | {
      | ^
foo.cc:36:2: error: expected '}' at end of input
   36 | }
      |  ^
foo.cc:6:1: note: to match this '{'
    6 | {
      | ^

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