/in/foo.cc: In function 'void dfs(int, int)':
/in/foo.cc:12:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0, v; i < G[u].size(); i++) {
                     ~~^~~~~~~~~~~~~
/in/foo.cc: In function 'void solve(int, int, int)':
/in/foo.cc:25:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0, v; i < G[u].size(); i++) {
                     ~~^~~~~~~~~~~~~