answer.code: In function ‘void dfs1(int)’:
answer.code:42:19: warning: structured bindings only available with ‘-std=c++17’ or ‘-std=gnu++17’ [-Wc++17-extensions]
   42 |         for (auto [v,w]:g[u]) if (v^Fa[u]) {
      |                   ^
answer.code: In function ‘void dfs2(int)’:
answer.code:49:19: warning: structured bindings only available with ‘-std=c++17’ or ‘-std=gnu++17’ [-Wc++17-extensions]
   49 |         for (auto [v,w]:g[u]) if (v^Fa[u]) top[v]=v,dfs2(v);
      |                   ^
answer.code: In function ‘void dfs(int, int, int)’:
answer.code:60:29: warning: structured bindings only available with ‘-std=c++17’ or ‘-std=gnu++17’ [-Wc++17-extensions]
   60 |         siz[u]=1; for (auto [v,w]:g[u])
      |                             ^
answer.code: In function ‘int build(int)’:
answer.code:67:19: warning: structured bindings only available with ‘-std=c++17’ or ‘-std=gnu++17’ [-Wc++17-extensions]
   67 |         for (auto [v,w]:g[u]) if (!st[v]) {
      |                   ^
answer.code: At global scope:
answer.code:111:1: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type]
  111 | main()
      | ^~~~
/usr/bin/ld: /tmp/cc4EUbVy.o: in function `main':
answer.code:(.text.startup+0x0): multiple definition of `main'; /tmp/ccAfzj9z.o:implementer.cpp:(.text.startup+0x0): first defined here
collect2: error: ld returned 1 exit status