/in/foo.cc: In function 'int main()':
/in/foo.cc:65:35: warning: iteration 1004 invokes undefined behavior [-Waggressive-loop-optimizations]
  for(int i = 1;i <= N;i ++) fa[i] = i;
                             ~~~~~~^~~
/in/foo.cc:65:18: note: within this loop
  for(int i = 1;i <= N;i ++) fa[i] = i;
                ~~^~~~
/in/foo.cc:64:37: warning: iteration 1004 invokes undefined behavior [-Waggressive-loop-optimizations]
  for(int i = 1;i <= N;i ++) head[i] = -1;
                             ~~~~~~~~^~~~
/in/foo.cc:64:18: note: within this loop
  for(int i = 1;i <= N;i ++) head[i] = -1;
                ~~^~~~