/in/foo.cc: In function 'void a_add(int)':
/in/foo.cc:38:26: warning: operation on 'anum' may be undefined [-Wsequence-point]
     ahead[a[anum].u]=anum++;
                      ~~~~^~
/in/foo.cc:43:26: warning: operation on 'anum' may be undefined [-Wsequence-point]
     ahead[a[anum].u]=anum++;
                      ~~~~^~
/in/foo.cc: In function 'int LCA(int, int)':
/in/foo.cc:104:26: warning: left operand of comma operator has no effect [-Wunused-value]
     ans=min((ans,dis[x][0]),dis[y][0]);
                          ^