/in/foo.cc: In function 'int main()':
/in/foo.cc:26:33: warning: iteration 30003 invokes undefined behavior [-Waggressive-loop-optimizations]
     for(int i=1;i<=mx;i++) fa[i]=i,num[i]=1;
                            ~~~~~^~
/in/foo.cc:26:18: note: within this loop
     for(int i=1;i<=mx;i++) fa[i]=i,num[i]=1;
                  ^