/in/foo.cc: In function 'll back1(int, ll)':
/in/foo.cc:34:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
/in/foo.cc: In function 'll back(int, ll)':
/in/foo.cc:46:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:58:17: warning: 'z' may be used uninitialized in this function [-Wmaybe-uninitialized]
  ll ans=0,x,y=0,z,m1=0;
                 ^