/in/foo.cc: In function 'int main()':
/in/foo.cc:22:19: warning: 'x' may be used uninitialized in this function [-Wmaybe-uninitialized]
  e[en].next=head[u];
             ~~~~~~^
/in/foo.cc:56:21: note: 'x' was declared here
    register int i,j,x,y,sz;
                     ^